Basics of RAID

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.'"

Holy Ads, bat-man!

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.

Re:Holy Ads, bat-man!

Looks ok to me - not a single one. Want my AdBlock list?

raid

http://raid.com/ [raid.com]
http://www.killsbugsdead.com/ [killsbugsdead.com]

Excellent RAID reference

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

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.

Or...

A source of information with far better content, that isn't simply an excuse to sell ads.

Wikipedia [wikipedia.org]

Current HDD prices...

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...

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...

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 a backup technique...

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.

Probably better

http://en.wikipedia.org/wiki/Redundant_array_of_in dependent_disks [wikipedia.org]

Give me RAID 5

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

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

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.

Another helpful link

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?

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.

Nice theory....

... 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.

Still a single point of failure

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

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$aver$.

Re:Still a single point of failure

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 controlle

Re:Still a single point of failure

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.

SCSI RAID Yes, IDE RAID No

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

There are two types of people:

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.

Windows RAID Over Firewire - Registry Setting

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.

My non-RAID backup solution..

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.