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Basics of RAID 242

Posted by Zonk from the brush-up-on-the-essentials dept.
Doggie Fizzle writes "RAID has been common in business environments for ages, and is now becoming more viable and popular for personal computers. This article focuses on the the basics of RAID, and spells things out for beginners or tech veterans. From the article: 'The benefits of RAID over a single drive system far outweigh the extra consideration required during installation. Losing data once due to hard drive failure may be all that is required to convince anyone that RAID is right for them, but why wait until that happens.'"
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Basics of RAID More

Basics of RAID

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  • Holy Ads, bat-man! (Score:5, Insightful)

    by temojen ( 678985 ) on Friday July 22, 2005 @06:41PM (#13140691) Journal
    That's an awful lot of ads for a re-hash of well-known info. Are the editors sure this is frontpage worthy? It looks like a blatant attempt to get page views to me.

  • raid (Score:4, Funny)

    by Anonymous Coward on Friday July 22, 2005 @06:41PM (#13140693)
    http://raid.com/ [raid.com]
    http://www.killsbugsdead.com/ [killsbugsdead.com]

  • Excellent RAID reference (Score:5, Informative)

    by Logic Bomb ( 122875 ) on Friday July 22, 2005 @06:42PM (#13140706)
    There's an excellent guide to RAID levels (with pretty diagrams and such) at http://www.acnc.com/raid.html [acnc.com]

    • There's a lack of real information about RAID (Score:4, Informative)

      by mollog ( 841386 ) on Friday July 22, 2005 @07:45PM (#13141081)
      I worked for years in development of RAID solutions for a major manufacturer. One of the problems with selling RAID solutions is the lack of understanding, or the prejudice and bias of the people who were supposed to be specifying and buying the hardware.
      The 'tutorial' of the parent article is talking in kindergarden terms, oversimplifications and obsolete term, and overlooking some of the issues with using RAID. It's a good example of the true lack of understanding about the subject. By now, there are so many types of solutions that the term RAID hardly applies. But, even 10 years ago companies like Compaq had innovative rudundant storage solutions that were enterprise ready.
    • Consider:

      RAID 10 disadvantage: "All drives must move in parallel to proper track lowering sustained performance". In fact each drive can seek independently for reads and only pairs must seek together for writes.

      RAID 1 advantage: "Transfer rate per block is equal to that of a single disk"
      RAID 5 disadvantage: "Individual block data transfer rate same as single disk"

      Would be nice if it was consistent about whether that's good or bad.

      RAID5: "Highest Read data transaction rate" except for RAID 10, of course,

  • Or... (Score:5, Insightful)

    by Joe5678 ( 135227 ) on Friday July 22, 2005 @06:43PM (#13140714)
    A source of information with far better content, that isn't simply an excuse to sell ads.

    Wikipedia [wikipedia.org]

  • Current HDD prices... (Score:4, Interesting)

    by Manip ( 656104 ) on Friday July 22, 2005 @06:43PM (#13140718)
    Depending on the your budget here in the UK you can get an 80Gb HDD for around £35, so split over some time you should be able to afford two (or an extra one if you already have one). This is a good enough reason for anyone to try RAID.

    I myself currently have it setup to mirror my data across two 80Gb drives... Four months ago one of the hard disks died (funny buzzing sound, no access) but the manufacturers three year warranty was still valid, so I returned the drive to them for a free replacement. I received the replacement drive and shoved it in, mirrored the data back onto this new second drive and continued as before. If I hadn't have had this setup that data could have been permanently list. It also saves me from writing ten DVDs to store that much.

    • Re:Current HDD prices... (Score:5, Insightful)

      by tool462 ( 677306 ) on Friday July 22, 2005 @06:53PM (#13140792)
      You may already know this, but it's worth mentioning to others who read this that may not. Your scheme works great to back up your data in the event of hardware failure, but in the event a virus or errant program corrupts the data, you'll still be wanting the DVD backups. That's because if a virus corrupts some files, it's doing the same thing on both drives, rendering the back up useless. RAID mirroring handles only one very specific type of data security. It's a very useful one, but it's important to understand the limitations or you can get bitten hard.

      Alternatively to DVD backups, you can also sync up your data on a regular basis to an external hard drive. This doesn't protect you if your house burns down, like DVD backups kept in a safety deposit box would do, but it does help you restore lost data after it gets corrupted.

      Ultimately, all these solutions require varying amounts of money, time, and effort, so you just have to decide what level of security you require and what you are willing to pay for it.

      • Re:Current HDD prices... (Score:5, Insightful)

        by ScrewMaster ( 602015 ) on Friday July 22, 2005 @07:27PM (#13140990)
        Ultimately, what it comes down to is that mirroring merely makes the hardware more reliable, it is not a backup technique.
        • Good point. Accidently delete or overwrite a file on a RAID array, and it's still just as hard to recover as if it were on a single drive.

        • It can be part of a backup technique... (Score:5, Interesting)

          by sczimme ( 603413 ) on Friday July 22, 2005 @09:24PM (#13141570)

          Ultimately, what it comes down to is that mirroring merely makes the hardware more reliable, it is not a backup technique.

          It can be part of this nutritious breakfast^W^W backup technique:

          0) shut down the box

          1) swap a fresh/new/wiped drive for one of the mirrored drives

          2) rebuild the RAID

          3) store the just-pulled drive appropriately (e.g. off-site) along with a second identical RAID controller

          Now if the machine goes completely belly-up (as in a fire) the user can install the secondary RAID controller and the data-laden drive in a fresh machine, add another fresh/new/wiped drive, and rebuild the RAID in the new machine. This may not be terribly convenient nor perfect for everyone but it will be effective.

          Remember, kids: just because a particular technique doesn't perform a task all by itself (in this case RAID 1 != backup) that doesn't mean it can't be part of a larger picture.

  • Give me RAID 5 (Score:3)

    by hobotron ( 891379 ) on Friday July 22, 2005 @06:44PM (#13140726)

    Seriously, SATA hotswappable RAID 5, put an onboard controller on next gen motherboards, I dont care if its crappy compared to an expansion card, and you will have my money. Yeah we have RAID 0, 1 , 0+1, but no onboard commercial RAID 5 solution in mainstream motherboards. I know its more expenisve, but its also more efficient, and with every failed HD common users encounter the market gets bigger.

    • Re:Give me RAID 5 (Score:3, Informative)

      by Ann Elk ( 668880 )

      Slightly OT, but this site [linux.yyz.us] is frequently updated with the current state of SATA/RAID support under Linux.

    • Re:Give me RAID 5 (Score:3, Informative)

      by kayak334 ( 798077 )
      I've been using this board [asus.com] from Asus for about 6 months with onboard SATA RAID5. It cost $120 from Newegg.com when I got it, if my memory serves me.

    • Here you go (Score:3, Informative)

      by kf6auf ( 719514 )

      I am running RAID 5 on my desktop server right here. It has a P4 3 year old Gigabyte motherboard. It's not hotswappable because it's not enterprise level (and I don't plan on having to hotswap all of the time, only when shit happens) but it gives me the RAID 5 that I like to use as a backup using software based RAID on Ubuntu Linux [ubuntulinux.org]. After the install, it it would be just as easy for Grandma to use as if it were not RAIDed and I am certain any /.er could figure out the install for most any Linux distro.

    • Personally, I'd be happy if the Linux kernel had a driver for my onboard Via SATA RAID controller, which I'm using for *gasp* RAID 0. Thing is, since Via has taken their sweet ass time providing drivers, I can't easily install Windows and Linux together on the RAID. Boo.

    • Re:Give me RAID 5 (Score:3, Interesting)

      by Nik13 ( 837926 )
      In the last while we've seen just about everything get incorporated on motherboards: USB2, Firewire, multichannel digital audio, GB Ethernet and everything else. I'm hoping RAID5 will be part of the next features to be added to most boards too. There's really not much else I'd want besides that.

      There's always software RAID5 too. It would sound like it's slower, but I'm not 100% sure about that (less cpu load for hw raid is pretty much a given though). The other consideration is what happens in a controler

      • Re:Give me RAID 5 (Score:4, Informative)

        by nmos ( 25822 ) on Friday July 22, 2005 @10:02PM (#13141765)
        These days I think software raid is really the way to go, at least in comparison to the raid built into consumer grade raid cards. With software raid you should be able to move your disks to a working computer and boot up with a Knoppix CD and access your data if you have to. You can also raid individual partitions rather than entire disks. You could make a small non-raid boot partition on each disk which you sync regularly plus a larger data partition which becomes part of the raid.

        The above applies to Linux, I don't think the non-server editions of Windows can do anything but raid 0 (maybe raid1?). Possibly a BartsPE CD could be used to recover a failed Win raid array.
    • No kidding. If I were a manufacturer of hard drives, I'd be _giving_ RAID-5 controller chips to motherboard manufacturers. Talk about increasing demand for your product.
    • Raid 10 needs 4 drives but a much less expensive controler. Adequate performance for Raid5 means a hardware XOR engine. Such a controler starts at about $150. A 4th 200GB drive is available for less than $100.

      RAID 10 is both faster and more reliable than RAID 5. (Though the chance on losing data for either is mighty low)

      RAID5 really only makes sense for arrays built out of the largest disks available.
    • I was thinking about doing something of that sort... but the specs for SATA PHY chips (so low-cost FPGAs without fancy IOs can be used) are somewhat scarce and most FPGAs with multi-gigabit transceivers cost over $200USD. (The elderly Xilinx XC2VP7 with 8xMGT currently costs ~$200 while the XC3S1000 which has 60% more logic capacity without the fancy IOs and PPC core costs $50.)

      A simple RAID solution can simply XOR the first two/four drive's data and store the result on the 3rd/5th drive. If any drive fail

  • RAID0 (Score:2, Informative)

    by fredistheking ( 464407 )
    RAID0 will increase your change of failure since you will loose all your data if a single drive fails. RAID0 isn't really redundant.
    • The array of disks is redundant. The data isn't. Seems like "RAID0" is an appropriate term for that.

      RAID0 isn't really appropriate for anything other than temporary files, anyway ... for exactly the reason you mention.

  • "now becoming more viable and popular for personal computers....Losing data once due to hard drive failure may be all that is required to convince anyone that RAID is right for them"

    I was thinking they were referring to "Joe Bob Home User" who is starting to use RAIDS more, which is true but, as far as I have seen they are NOT using it for RAID1 - (Mirroring and Duplexing) they ARE using it for RAID 0 (Striping) so their system apps/games run faster.

  • Another helpful link (Score:5, Funny)

    by Toasty16 ( 586358 ) on Friday July 22, 2005 @06:46PM (#13140737) Homepage
    Here is a link that explains the basics of computer hardware; I think that it's a good companion piece to the RAID article: http://www.angelfire.com/rings/judy_patch/ [angelfire.com]

  • RAID for "personal computers"? but why? (Score:5, Insightful)

    by Rosco P. Coltrane ( 209368 ) on Friday July 22, 2005 @06:46PM (#13140739)
    Okay I guess it appeals to geeks and fancy computer modders and all. But really, when it comes down to it, a decent main hard-disk, a tray in the second bay for backup hard-disks, and a reasonable backup regimen that people keep up is all a "personal" computer user needs.

    Personally, I have 3 backup hard-disks, one that keeps a "clean" base system that I update every 6 months or so, and 2 that I do full differential backups on every 3 days. The "clean" hard-disk is kept off-site, and a script tells me when to do the backups on the other 2. And for very very important files, I just write them on a CD on the spot.

    With that, I've yet to lose a single file since I started using Linux in 93 or 94. My solution is cheap and doesn't involve fancy raiding. And I'm quite sure I overdo it, most people could do just fine with one main hard-disk, one backup hard-disk and a little discipline.
    • Comment removed based on user account deletion

    • Nice theory.... (Score:4, Informative)

      by dbc ( 135354 ) on Friday July 22, 2005 @07:04PM (#13140850)
      ... but how often do personal backups actually happen? I'm one of those guys that has been taking home backups seriously for a long time, and has a collection of obsolete tape units to prove it. And backups still do not happen often enough if it requires me handling tape.

      Let's face it, discipline is a drag, that is why at work IT people are paid to schlepp around stacks of locked cases full of back up tapes to be shipped off site.

      So... for my home file server, I went to RAID mirroring, with a 3rd drive in a drawer. A mount-copy-umount chron job copies to the drawer-drive. Drawer-drive gets swapped and taken off site "when I think of it". Because... RAID only protects you from falling over hard drives. It does not proctect you from:

      1) Ooops, I wish I hadn't deleted that.
      2) Gack! My house just burned down! And took 10 years of tax data with it!
      3) Power supply goes wonky, causing both drives to scribble random scorfulentness everywhere.

      A home RAID system does not need to be expensive. Who needs hot swap? Use cheapo PATA drives. A few hours of down time for the wife and kids is OK. It doesn't take a big, bad CPU, and software RAID works great.
    • How about this.

      You do RAID 1 with 3 disks instead of 2. Two drives are for the RAID 1 setup and when it's time to do the backup you just power down or "prepare for hotswap", take out one of the RAID 1 drives which is now your newest backup and put the third drive back into the RAID.

      You wouldn't have to do "full differential backups every 3 days" anymore.

      Only think I've yet to look into, before I do this, is how to tell the RAID which of the drives it needs to update and which to mirror from. Wouldn't wan

    • and a reasonable backup regimen

      Ah, but that is the rub, is it not? Many people are using mirrored arrays as an excuse to not backup.

      The university department I work for has a faculty member that teaches this through his actions. He claims everyone should backup (to cheap CDR's and DVD's mind you) and all of his workstations, and any students he has assisted with a purchase uses a Promise RAID1.

      Some of those machines have returned for assistance with issues, and I have seen some pretty odd hacks

  • With RAID, you still have a single point of failure. Instead of it being your hard drive, it is now your RAID controller. So what is the advantage?

    Since a RAID controller doesn't have moving parts, is it less likely than a hard drive to fail?

    • Re:Still a single point of failure (Score:4, Insightful)

      by Rick Zeman ( 15628 ) on Friday July 22, 2005 @06:51PM (#13140780)
      With RAID, you still have a single point of failure. Instead of it being your hard drive, it is now your RAID controller. So what is the advantage?

      You get a new one under warranty or buy one...and your data is still there. If your drive dies and you get a new one your data's toast unless you have megabucks for Drive$aver$.
    • With RAID, you still have a single point of failure. Instead of it being your hard drive, it is now your RAID controller. So what is the advantage?

      For a home RAID system, the advantage is you can replace the RAID controller and still have all of your data. Unless of course the RAID controller corrupts all the data, but I'm not sure I've ever seen that happen.

      • Re:Still a single point of failure (Score:4, Informative)

        by PhotoBoy ( 684898 ) on Friday July 22, 2005 @07:03PM (#13140847)
        I've had my data corrupted by a dodgy controller... twice. I've been having terrible luck with the nvRAID provided on nVidia nForce 4 motherboards. Twice now the machine has locked up and on rebooting the RAID array is reported as damaged and a drive is missing from the array. A bit of Googling has revealed it's a common problem.

        Fiddling around in the BIOS disabling and reenabling RAID makes both disks show up again but putting them back into a RAID array seems to do no good as Windows always claims files are missing after doing this. If I reinstall Windows my data is always all still there in perfect condition, the hassle of reinstalling Windows and my apps is a pain though. So it's not totally corrupted, but enough to be a complete bitch.

        My feeling on RAID on the desktop is that it's a good idea but at least in nVidia's case it's being done on the cheap and is not totally stable. That said Intel's RAID controllers are superb and I'd use one anyday if it weren't for the vast amounts of heat and inferior performance of the P4.
    • Yes.

      The controller's still a point of failure. Indeed, with some RAID controllers if they go bad they corrupt data on *both* your disks, rendering both unusable.

      RAID protects against hardware failure of a drive.
      It does not protect against a bad controller or an OS snafu (for example, I once had the MSFT go bad on an NTFS volume, losing all data on a drive. RAID wouldn't have helped me there, either).

      So if you really care about your data, you should run RAID in conjunction with an off-disk backup solution
    • > With RAID, you still have a single point of
      > failure. Instead of it being your hard drive,
      > it is now your RAID controller. So what is
      > the advantage?

      What kind of failure you mean? You mean getting your data damaged due to RAID controller failure? I've never heard of something like that but maybe it may happen. But I can bet that it will happen less than harddrive failure - so still having N drives and one controller is less likely to fail than having one hd - means RAID has advantage here...
    • Instead of it being your hard drive, it is now your RAID controller. So what is the advantage?

      Your RAID controller isn't who saves your data, so you don't lose your data, which is the point of several RAID modes?
    • Our most critical stuff is mirrored on seperate disks that are on seperate backplanes attached to seperate controllers. So the only single point of failure is the system, and if it goes down well the data isn't that useful anyhow.

      Also yes, RAID controllers are much less likely to fail. For the most part, if a solid-state device works for the first 30 days, it'll work forever if it's taken care of. There are exceptions, of course, but lacking any moving parts there just aren't a lot of ways for them to wea

      • For the most part, if a solid-state device works for the first 30 days, it'll work forever if it's taken care of.

        You are quite wrong about this. Electronic devices have known failure mechanisms which determine the useful life of the device.

        IC designers are most concerned about electromigration these days. Electromigration causes the metal in the metal traces on chips to be moved from one location to another, causing thinner metal lines. Eventually this will cause the device to fail.

        Most mechanisms t

    • That and when a RAID controller breaks, you can replace it with another one with down time but no data loss. When a hard drive breaks, you can replace it but you lose the data.
    • Yes and No.
      For a basic RAID, ie a host card in a computer attached to a bunch of disks, then yes, the card is the single point of failure. This is less of a problem than losing a disk because: the card is less likely to fail (as you guessed, no moving parts) and failure of the card doesn't necessarily mean loss of any data. Failure of the RAID card will mean access to the attached RAID array becomes difficult =) however some machines even have hot-swap adapter cards, in which case you swap out the card for
    • It depends on what you call failure. If failure is losing data, then it's not a SPOF. If the failure is availability, then you wouldn't use RAID to save yourself. You'd use a high-availability cluster. When the controller fails, you fail over to another node with replicated data.
    • With RAID, you still have a single point of failure. Instead of it being your hard drive, it is now your RAID controller.

      That's why you use software RAID for scenarios where you can't afford to keep a spare controller on the shelf, a decent warranty, or simply want the greater flexibility and reliability.

    • With RAID, you still have a single point of failure. Instead of it being your hard drive, it is now your RAID controller. So what is the advantage?

      Since a RAID controller doesn't have moving parts, is it less likely than a hard drive to fail?

      A real RAID controller (not one of those crappy software-assisted RAID controllers; eg, anything under $400 or built onto a consumer-grade motherboard) is several orders of magnitude less likely to fail than your hard drives are. And even the best hard drives -

      • Suppose you have two disks and "software assisted" motherboard RAID, Would it be better to hook them up as separate disks or as a raid then?

        • Suppose you have two disks and "software assisted" motherboard RAID, Would it be better to hook them up as separate disks or as a raid then?

          By all means, RAID them if you'd like - but don't trust them with anything crucial unless you really understand the recovery process. And by understand, I mean do it once or twice with a configuration you don't mind using, until you are confident you know the quirks of getting back up and running - especially with Linux (and simulate failing BOTH disks!).

          Having

        • It all depends on your needs. Several posters above have provided good links to RAID info; check them out.

          If you need storage space, just use independent disks. If you need speed for streaming data, use RAID 0 (but be aware that your speed will be severely curtailed by your software-assisted controller). If you need switch-over backup in case of disk failure (usually, servers need it, so that they can keep on carrying out their tasks), use RAID 1. (Do NOT use RAID 1 as a replacement for periodic backups

    • I have always used RAID M you have more then one HD in your system and you copy what ever is important to more then one drive. Since I use a Mac i also have the OS on other drives so if my OS gets toated I just boot from a different drive. Works for me for the last 10 years.
    • data redundancy.

      you don't get that with two power supplies or two keyboards.

  • Money talks (Score:2, Informative)

    by cazbar ( 582875 )
    Losing data once due to hard drive failure may be all that is required to convince anyone that RAID is right for them, but why wait until that happens.

    Cuz the boss won't cough up the money until it happens.

  • Too expensive (Score:2, Insightful)

    by pete19 ( 874979 )

    As a (poor) student, I find that I simply can't afford an extra hard drive! I got a 2nd hand DVD burner from a friend for £15 and backup all my really important stuff (Code for university, photos, etc) every week. All my MP3s go on another DVD along with the hard disk, and they're "backed up" on my MP3 player anyway.

    As of yet I've never had a single hard disk failure... but I've not really got anything I'm bothered about losing, so RAID isn't worth it for me.

    • You're fine with that, and you're right: RAID isn't worth it for you.

      RAID isn't trying to solve your problems, anyway. Most RAID configurations are trying to provide higher rates of speed OR instantaneous fail-over solutions for servers. Not to worry!

  • SCSI RAID Yes, IDE RAID No (Score:5, Funny)

    by Anonymous Coward on Friday July 22, 2005 @06:51PM (#13140779)
    IDE HDD Talking to IDE Controller:
    HDD: I'm gonna need more time for that write
    Contr: Yeah OK, go ahead good buddy
    Contr: What's up?
    Contr: What's up?
    Contr: Error: Drive controller timeout error

    SCSI HDD Talking to SCSI Controller:
    HDD: I'm gonna need more time for that write because I found a bad block
    Contr: Yeah OK, go ahead and remap that bad boy
    Contr: What's Up?
    HDD: Need more time to map that bad block
    Contr: Yeah OK, go ahead
    HDD: All done, grabbing the next command in the queue
    • IDE drives have had sector remapping for _at least_ 10 years now.

    • Speaking of SCSI features, NCQ is now available on some SATA drives. It's not the full blown SCSI version, from what I gather, but it does bench well. See Tom's article [tomshardware.com] on it.

      I have two RAID controllers populated with two drives each in RAID-0. One has two of Western Digital's Raptors (74GB 10,000 RPM). The other with two of Maxtor's DiamondMax HDDs(250GB 7200 RPM). The latter has NCQ and benches significantly better. Some of the difference may be related to one RAID controller being better than the

  • Personally, I prefer daily backups to another HDD (use rsync, it's great), that way, if I make a major *oops* during the day I know I have a very recent backup immediately available, this is something that RAID cannot protect you from (the human failure).

    If then I've still got money to spare, I'll look at mirroring.

    http://www.mikerubel.org/computers/rsync_snapshot s / [mikerubel.org] is a great page to learn about using rsync to make easy backups.
  • There are two types of people: Those that have lost data, and those that will.

    Don't forget, though kids - RAID won't protect you from deleting your own data, or a malformed script trashing stuff.
  • Choose your Raid [raid.com] Click on which type of raid you want to know about, and it tells you what its good for, disadvantages and advantages.
  • For those who have run out of internal space in their boxes, and who don't have external SATA or expensive hardware boxes, you can run RAID over Firewire.

    The problem, however, is that out of the box Windows refuses to "promote" an external disk to dynamic, which is required on all post-NT4 rigs for RAID.

    The solution is to add a semi-documented Registry flag, EnableDynamicConversionFor1394 [google.com].

    HOW TO: Convert an IEEE 1394 Disk Drive to a Dynamic Disk Drive in Windows XP [microsoft.com]

    Couple that with a cheap 4-bay firewire JBOD box and any spare old enclosures and you are set!

    I run 2TB in various RAID configs on my Windows server (main and near-line storage). Have done so since 2002. No problems with the external boxes. The support for external firewire RAID is a little gnarly in Windows 2000 - volume must be mounted as a named virtual directory and cannot be mounted as a letter drive. Later Windows give you both options.

  • With hardware cost falling steeply, when will it become viable for home users to start having RAID-based PCs?

    All said and done, many of us do keep fairly important data on our home PCs. How many of us make an effort to back it up?

  • RAID 0+1 vs RAID 1+0 (Score:3, Informative)

    by georgewilliamherbert ( 211790 ) on Friday July 22, 2005 @07:18PM (#13140930)
    This is a non-trivial question:

    When you're setting up a RAID set using both striping and mirroring, do you want to set up two stripes and then mirror between the stripes (0+1), or do you want to set up mirrored pairs and then stripe those mirrored pairs (1+0)?

    This is a quiz, and your data will grade you.

    What you want, by far, is RAID 10 (1+0).

    When you set up two stripes and then mirror across them, if you lose two disks, any disk in the first stripe and any disk in the second stripe, you lose all the data.

    If you stripe across mirrored pairs, then the only way to lose data is to lose both drives in one of the mirrored pairs. You can lose any other disk than the second drive in a pair, or even many more disks, as long as they aren't both in the same mirrored pairs.

    This doesn't make a difference with 4 drives. At 6 drives and up, use 10. Your data and users will thank you for it.

    • Keep one thing in mind about adding more drives.. Mean Time Between Failure falls as a function of how many drives you are using. If the drives are rated at 50,000 hours MTBF and you run a 2-drive mirror, you now have a MTBF of 25,000 hours on the array (not on a single drive). Likewise 4 drives would drop it to 12,500 hours. This is not a bad thing, just expect that with more drives spinning, the odds that one of them will woof is greater. Law of averages kinda thing.

      • Keep one thing in mind about adding more drives.. Mean Time Between Failure falls as a function of how many drives you are using.

        Correct.

        Unless you need high performance (Database spindle count, for example), using as few drives as possible saves on expensive RAID controller or RAID unit chassis slots, and improves MTBF of the set of disks.

        Home users won't typically care, they want minimalist solutions, only talking about a few drives.

        Enterprise sysadmin / data managers care; when you get up

  • I had my system hard drive fail fatally on me, emails and so forth, only some random backups elsewhere. Right then and there I decided that no more will a hdd failure steal my stuff from me and bought 4x120gb drives (size/price ratio at time was optimum) and a Promise controller. Now I got ca. 240gb RAID 01 setup, mirroring gives reduncancy and striping keeps the array at least as fast as those drives used separately.

    One hdd did fail on that array, and I just replaced it with warranty replacement hdd. No h

  • A lot of motherboards come equipped with RAID capabilities even if the end user doesn't know what the acromym means.

    Now that external USB/Firewire drives have become more affordable as a backup solution, I recommend that. Confession: I don't know WTF I am talking about.
    • I don't know of any mainstream desktop boards that offer any more than 0/1/0+1, which is either unreliable (0) or inefficient (1/0+1).

      RAID 5 is what you want, it's just bloody expensive to get it (in hardware) at the moment. If one of your drives fails, you just take it out, stick in a replacement and it will rebuild the array for you from the parity information on the other drives. Fast read/write and good redundancy.
  • At one time, I thought RAID was teriffic. But honestly, I think it's way over-rated and exists primarily for the benefits of systems builders and manufacturers to sell people additional hardware and increase their profits.

    1. RAID implementations on most consumer-grade motherboards (EIDE RAID with Promise controllers on-board, and so on) are cheezy. I've tried using them for several years now, and I ran into lots of unexplainable "glitches" that never occured when I took RAID out of the equation. (EG.

  • RAID is really here (Score:2, Informative)

    by JB72 ( 463516 )
    It's amazing how common RAID is now, especially (S)ATA RAID.

    In video editing, RAID is everything. External SATA RAID is the big thing now, and it works pretty well, even when it's OS based. What I haven't seen yet are (relatively) cheap SATA RAID 5 enclosures. That would be the Holy Grail of fast media storage.
  • I've fiddled with raid a bit but haven't yet had enough failures under my belt to know how raid systems behave in real-world drive failures. Can somebody comment on their experiences for the following hardware configs:
    • What happens when, say, an IDE drive fails using software raid on linux? Does the machine stay alive, or do you need to remove the drive and reboot to get back to working?
    • How about failures with full hardware raid, like an LSI megaraid card. I've unplugged a drive with one of these and
    • I've been using software-RAID with ATA drives on Linux for quite some time, so I can comment on the behaviour of an array containing a faulty drive.

      First off, let me emphasize how important it is to set up proper email notification (or pager etc.) for such cases! If you don't know about the failure, you're certain to get nice phonecalls from affected users.

      If you've set up the notification system (smartd and mdadm come to mind), you'll eventually get an email saying something like "Device: /dev/hdc, ATA e
  • As a future project, I was thinking of building a RAID 5 solution from stock parts, but then I came across this

    http://www.lacie.com/products/product.htm?pid=1032 6 [lacie.com]

    Which seems not to be much more expensive than building your own. The same company has a nice line of other desktop and network drives (I have no connection to this company whatsoever).

    Drawbacks?
  • You don't need backups if you don't do anything important. I should know. I am an official member of RAID - Redundant Army of Independent Derelicts. Of course, before PC (political correctness), back in my day, we just called ourselves HOBOS. (Huge Obnoxious BO Smellers). One day, I was wetting myself and talking to God, and he said, "Jed, get away from there, you don't need no RAID. Black gold, Texas tea.", Next thing you know, I'm a Lotto (TM) millionaire. So, I went to California and started a dot-com
  • Has anyone tried using Linux Software RAID and a bunch of external USB drives? I'm wondering what the performance would be like for a light-duty file server. I want to go from a huge case to much smaller case, and that means getting the RAID drives out of the case.

  • raid for desktop - not really worth it (Score:3, Interesting)

    by vlad_petric ( 94134 ) on Friday July 22, 2005 @09:09PM (#13141517) Homepage
    RAID makes a lot of sense in a server scenario, where uptime is crucial, and where the cost of hardware is smaller than the business lost by downtime.

    As far as desktops are concerned - well, RAID and cheap just don't mix. For instance, if you just want reliability, RAID 1 is enogh (2 drives). If you want reliability + fast writes, you need RAID 1+0, which means 4 drives (RAID 5 only gives faster reads). Furthermore, a good controller is crucial (from my experience, these generally cost upwards of 100$).

    Finally, RAID does not subsume in any way a good backup system. I've seen cases where a damaged controller broke both harddrives in a RAID 1. However, for (most) desktop PCs, a good backup system does subsume RAID, since it's generally easy to just use a different computer, and get all the files from the backup.

    For me, the excellent piece of software backuppc [sf.net] running on a cheap box (~300$) has worked like a charm. This might not look cheaper than RAID, but considering that I'm using just one box to back up 10 other machines, it's pretty good.

  • My non-RAID backup solution.. (Score:4, Interesting)

    by the_rajah ( 749499 ) * on Friday July 22, 2005 @09:21PM (#13141561) Homepage
    No, it's not "Real-Time" but it suits our needs in our home office situation.

    I use "Smart Synch" software to incrementally copy the desired directories from the working computers to a "Backup server", an older Celeron machine on the network. Separate partitions are set up for each computer that is being backed up. At Midnight the incremental backups are made.

    Then at 2:00 a.m., Smart Synch running on the backup server makes another backup to a USB hard drive plugged into it. That USB HD is on a regular plug-in timer so that it only runs during the time of night when a backup to it is being done. The idea there is that the running time is limited and drive life is extended. Weekly, a backup DVD is burned and stored off site. Am I being anal? Maybe.
  • I mean if you just want fault tolerance then use straight up mirroring. If it's for currency then perhaps you need a journalling file system with checkpoint rollback/rollforward.
  • My father has trusted his data (against my advice) to fakeraid chipsets on his various motherboards twice. He just got done *losing* all of his data for the second time.

    Best we can tell, he had one drive go without his RAID controller warning him; then had a second drive go, killing the array. He spent weeks with a dead PC playing with all kinds of special Windows bootloaders and disk recovery tools trying to get his files back.

    Fakeraid sucks because it's just a line item on the sale of a modern motherboa

  • Why wait? Everybody waits.. (Score:3, Insightful)

    by Man in Spandex ( 775950 ) <prsn@kev.gmail@com> on Friday July 22, 2005 @09:57PM (#13141731)
    Losing data once due to hard drive failure may be all that is required to convince anyone that RAID is right for them, but why wait until that happens.'"

    Isn't it human nature (or at least that's what it seems) to wait until something "bad" happens?

    That goes for obese people, smokers and yes even computer geeks.

    Why eat all the fat? I'll just burn em all!
    - Wait til your 40-50 and check that cholesterol strike...

    So many people smoke and get away with it so I will to right?
    - Yeah wait til you get some health problem that will make you say "OH NOES!"

    Why I need firefox? ActiveX hasn't screwed me.
    - A week later "omfg whats all this junk, I want Firefox!"

    Why Do I need RAID or even a burner? I got 3 hard drives that contains all my data!
    - 8 months later, 1 hdd crashes "AH F*K ALL MY Pr0n!" and then he thinks of having a simple RAID 1 setup...

    We always wait because we are lazy and cheap.

  • the article is full of errors (Score:3, Informative)

    by erc ( 38443 ) <erc@[ ]ox.com ['pob' in gap]> on Saturday July 23, 2005 @12:17AM (#13142352) Homepage
    One glaring error:

    RAID can be run on any modern operating system provided that the appropriate drivers are available from the RAID controller's manufacturer. A computer with the operating system and all of the software already installed on one drive can be easily be cloned to another single drive by using software like Norton Ghost. But it is not as easy when going to RAID, as a user who wants to have their existing system with a single bootable hard drive upgraded to RAID must start from the beginning. This implies that the operating system and all software needs to be re-installed from scratch, and all key data must be backed up to be restored on the new RAID array.

    Again, wrong, wrong, wrong. There are hardware RAID 1 controllers that require no drivers and you don't have to do squat - just power down the server, install the RAID 1 on your IDE interface, plug in the new drive, hit the power, and away you go. The controller is smart enough to automatically sync up the two drives in the background.

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