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Serial SCSI Standard Coming Soon 328

rchatterjee writes "SCSI is very close to joining ATA in leaving a parallel interface design behind in favor of serial one. Serial attached SCSI, as the standard will be known, is expected to be ratified sometime in the second quarter of this year according to this article at Computerworld. Hard drive manufacturers Seagate and Maxtor have already said that they will have drives conforming to the new standard shipping by the end of the year. The new standard will shatter the current SCSI throughput limit of 320 megabit/sec with a starting maximum throughput of 3 gigabit/sec. But before this thread turns into a SCSI fanboy vs. ATA fanboy flame war this other article states that Serial Attached SCSI will be compatible with SATA drives so you can have the best of both worlds."
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Serial SCSI Standard Coming Soon

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  • by Anonymous Coward on Sunday March 09, 2003 @06:20PM (#5473011)
    The current parallel SCSI is 320 megaBYTEs per second, which is 2.56 gigaBITs per second.
  • bits vs. bytes (Score:5, Informative)

    by David Jao ( 2759 ) <> on Sunday March 09, 2003 @06:20PM (#5473013) Homepage
    Guys (meaning submittors and editors), the current version of SCSI delivers 320 megabytes [] per second of interface transfer rate, not megabits.

    320 megabytes is about 2.5 gigabits ... which is a lot closer to 3 gigabits than the erroneous 320 megabits figure.

  • Re:Mbit != MByte (Score:2, Informative)

    by Anonymous Coward on Sunday March 09, 2003 @06:24PM (#5473026)
    Actually, that's 320 Megabytes per second for Ultra 320 SCSI and 3 Gigabit per second (approx 375 Megabytes per second) for Serial Attached SCSI
  • U320 SCSI (Score:2, Informative)

    by Unix_Geek_65535 ( 625946 ) on Sunday March 09, 2003 @06:25PM (#5473031)
    Greetings fellow geeks :-)

    U320/LVD SCSI is capabable of 320MB / sec not 320mbps.

    3gbps ~= 300MB/sec. therefore it would not be be quite as fast as U320 SCSI.

    Naturally 320MB/sec is the theoretical max bandwidth for the SCSI bus not the individual drives in the SCSI chain.

    Live long and prosper
  • For more info (Score:3, Informative)

    by Anonymous Coward on Sunday March 09, 2003 @06:29PM (#5473048)
    For more info on Serial attached SCSI check out this page: d.html []
  • Re:SASCSI (Score:5, Informative)

    by Ryan Amos ( 16972 ) on Sunday March 09, 2003 @06:30PM (#5473058)
    To reduce crosstalk between the wires so that you can run at faster speeds. Indeed, the "rounded" IDE cables often reduce performance by 5% or so. We're getting better at data throughput though, so we can use serial technologies and actually get faster transfer rates. Good riddance to ribbon cables :P
  • Re:SASCSI (Score:5, Informative)

    by shepd ( 155729 ) <> on Sunday March 09, 2003 @06:31PM (#5473067) Homepage Journal
    >Why not simply roll the ribbons up into cables?

    Impedance, crosstalk (mentioned) and price.

    It takes seconds to crimp a ribbon cable. Cheap and easy. You can even do it yourself!

    Taking a bunch of twisted pair wires (which is what would be required to keep the impedance and crosstalk bearable) and soldering them onto connectors individually takes a lot more effort, and therefore costs more.

    Not to mention fabbing individual strands of insulated wire and twisting them together costs more than running 5 wires parallel to each other and simply coating them all at the same time with PVC.
  • Re:Is this a trend? (Score:5, Informative)

    by TheShadow ( 76709 ) on Sunday March 09, 2003 @06:40PM (#5473109)
    I don't think so. The reason there is a tremendous push towards serial right now is because parallel interfaces create more interference at higher frequencies. The theory with serial is that you can push the frequency as high as you want without the interference.
  • by jdoff ( 95905 ) on Sunday March 09, 2003 @06:43PM (#5473118) Homepage
    You're mistaken. It's Small Computer System Interface. See []
  • by Zebra_X ( 13249 ) on Sunday March 09, 2003 @06:43PM (#5473121)
    PCI Plus proposed by Intel is promising 2GB/sec dedicated channel per device on the PCI Plus bus.... this doesn't fully meet the needs of the drives but is certainly a step in the right direction.
  • by aussersterne ( 212916 ) on Sunday March 09, 2003 @06:45PM (#5473132) Homepage
    SCSI: Small Computer Systems Interface

    descended from

    SASI: Shugart & Associates Systems Interface
  • by ChaosMagic ( 657047 ) on Sunday March 09, 2003 @06:46PM (#5473135)
    I don't know the technical details but I would imagine that in a virtual world where everything worked in theory, you'd be right, parallel would be faster. It stands to reason that however fast you can get a serial link, you can just put it together with a few more and have a parallel one just as fast.

    I think the problem(s) come when you have to take into account keeping parallel lines in synch with one another, accouting for lost bits, and breaking down/putting back together all the information at either end. This all adds up in overhead for a parallel connection, where a serial connection just lets the information go through the line with little or no pre/post processing or synching to worry about.
  • by torre ( 620087 ) on Sunday March 09, 2003 @06:54PM (#5473175)
    With PCI-X 1066 [] 8.6GB/s bus tranfers are possible so that should be too much of a problem. Also, the InfiniBand [] aims to solve that problem. One can see that 6GB bus' were planned even in this older dell whitepaper [] suggests.
  • Re:Firewire? (Score:5, Informative)

    by torre ( 620087 ) on Sunday March 09, 2003 @07:02PM (#5473212)
    SCSI is expensive, FireWire is proven technology. Wouldn't it be more sensible to use FireWire? []

    Firewire is low end consumer product...even with its successor (which is taking longer than expected to ship) running at 800Mbits/s (100 Megabytes/second) it falls short of current SCSI technology running @ 320MB/s. As such there is no one who would seriously consider firewire for a large scale server handling many gigabytes/terabytes of data. Firewire is just too slow of a bus for big needs, but does fills its convenience needs in the consumer market. Everything has it's own niche... that's why heavily marked up servers/mainframes/supercomputers still exist instead of cheaper home machines which just can't fill the requirements.

  • Re:Benefits of SCSI? (Score:2, Informative)

    by khuber ( 5664 ) on Sunday March 09, 2003 @07:09PM (#5473246)
    Better drives that are designed to run 24/7 with load. The drives usually have lower seek times/lower rotational latency. Some of this comes at the cost of heat and noise which Joe Consumer might not tolerate. Seek times are incredibly underrated, btw. The SCSI interface itself really doesn't have much advantage over ATA, but the industry builds its best drives for SCSI/FCAL.
  • Re:Benefits of SCSI? (Score:2, Informative)

    by MoralHazard ( 447833 ) on Sunday March 09, 2003 @07:13PM (#5473266)
    There is no "hard-limited" maximum of 4 IDE drives per motherboard. Most boards have two IDE channels built in, and IDE will only support 2 devices per channel, so you get four devices from the board. However, you can buy many, many boards that have more than that, especially lately (Abit's AT7/IT7 models come to mind).

    Most board manufacturers include only two IDE channels because that's how many are generally built into north-bridge chipsets. The Abit boards mentioned above use an additional Promise HPT374 chip to provide FOUR extra IDE channels, for a total of TWELVE IDE devices, altogether.

    If you want more IDE devices than your board supports natively, you can just buy PCI cards that have more IDE channels. Promise, SIIG, and Highpoint all make really cheap cards that have an extra two channels, or four more devices.

    SCSI limitations are similar. You only get 15 devices PER BUS, but you can add as many devices into your system as you have PCI slots and IRQs for. You can buy an Adaptec 29160 card (dual busses) and plug 30 hard drives into it. Buy four of them, and can have more than 100 drives.
  • by Anonymous Coward on Sunday March 09, 2003 @07:26PM (#5473314)
    crosstalk!!!!! current running through a wire creates magnetic fields that affects neighbouring wires...if there's only one wire, there's less interferance.
  • by lederhosen ( 612610 ) on Sunday March 09, 2003 @07:38PM (#5473373)

    At what clock speeds does HyperTransport(TM) technology operate?

    HyperTransport(TM) technology devices are designed to operate at multiple clock speeds from 200MHz up to 800MHz, and utilizes double data rate technology transferring two bits of data per clock cycle, for an effective transfer rate of up to 1,600Mb/sec in each direction. Since transfers can occur in both directions simultaneously, an aggregate transfer rate of 6.4 Gigabytes per second in a 16 bit HyperTransport(TM) I/O Link and an aggregate transfer rate of 12.8 Gigabytes per second in a 32-bit HyperTransport(TM) I/O Link can be achieved. To allow for system design optimization, the clocks of the receive and transmit links may be set at different rates.


    For the pentium4:

    133MHz Quad Pumped (533MHz effective) allowing access to up to 4.2GB Bandwidth

    But I guess that most of the trafic is mem-hd
    or hd-mem and thus does not nead to go trough
    the cpu, I think the latest alphadesign was
    to have 8 rambus chanels giving plenty of
  • by 0x0d0a ( 568518 ) on Sunday March 09, 2003 @07:39PM (#5473383) Journal
    Those numbers *sounded* completely wrong.

    Existing SCSI is 320Mbps*8bits/byte = 2.5Gbps.

    Moving to 3Gbits is evolutionary, not a huge jump.

    I'm wondering what's going on here too -- WTF happened to Firewire? I remember thinking that everyone would be using it as a universal high bandwidth data bus, and for some reason it doesn't seem to be happening.
  • A couple of notes (Score:4, Informative)

    by Jordy ( 440 ) <jordan AT snocap DOT com> on Sunday March 09, 2003 @07:40PM (#5473391) Homepage
    There are a couple important notes about Serial-attached SCSI (SAS) that I think are important.

    First, SAS uses a point-to-point topology similar to Serial-ATA instead of a shared bus like SCSI. This means each drive has access to full bandwidth, not just one (the bottleneck being the card itself).

    Second, according to the SAS working group, SAS comes in three speeds; 150, 300 and 600 MB/s. I'm not sure where that 3 Gbps figure came from.

    Third, unlike Serial-ATA or parallel SCSI, SAS is full duplex like fibre channel. This should have some interesting effects on latency.

    Fourth, SAS uses the same physical connector as Serial-ATA and in fact can use Serial-ATA drives in legacy mode.
  • by Anonymous Coward on Sunday March 09, 2003 @07:43PM (#5473415)
    Serial Streaming Architecture that is. It's a 40MBps serial hardware layer that runs SCSI protocal. It's configured in a loop so there's automatic redundancy in case one link gets disconnected. And a single segment can be up to 20 meters long. Anyone have a Shark (ESS)? It's all SSA inside.

  • by ozzee ( 612196 ) on Sunday March 09, 2003 @07:48PM (#5473444)
    What 10Gbit Ethernet? Obsolete Ethernet is 10Mb. Typical current Ethernet is 100Mb. Up and coming 1Gb Ethernet is appearing.

    Where have you been ? I've been using 1000BaseTX ethernet for over a year. Right now I would only buy a machine with a GigE port. The switches are still a little pricey but they will come down.

    10 Gbit was ratified last year. See here []. It's only multimode fibre though.

  • Re:Benefits of SCSI? (Score:3, Informative)

    by drsmithy ( 35869 ) <> on Sunday March 09, 2003 @07:50PM (#5473451)
    I keep hearing that SCSI drives are better for hardcore media editing and for servers, but I'm curious why. Is there a compelling advantage for desktop users (or even servers)?

    For desktops, not really. For server, yes. SCSI, due to (generally) lower latencies, higher rotational speeds and a smarter interface destroys IDE in high-load multi-user style scenarios (lots of random reads & writes all over the disk). Very few (if any) desktop users generate the sort of usage patterns that allow SCSI to shine, so on the desktop it has little advantage (particularly taking into account the cost).

    Most people who say SCSI gives them a good boost on their desktop machines are usually comparing quite new SCSI drives to quite old IDE ones, are dealing with poorly-configured IDE setups (more than one device on a channel) or are using an older, slower machine (probably with a crappy IDE controller). For the vast, vast majority of users (and that includes high-end users) SCSI offers little benefit.

  • Re:SASCSI (Score:2, Informative)

    by dotgain ( 630123 ) on Sunday March 09, 2003 @08:08PM (#5473535) Homepage Journal
    External SCSI cables aren't ribbons, and work fine. You can't use any old 50 core cable, I think all the pairs inside them are twisted together.

    I have a 10M SCSI ribbon, and each pair is twisted. I think the main reason for ribbons inside the box is so you can crimp on a connector wherever you want. Oh, and in a Sparc20, the internal SCSI cable isn't a ribbon, it's a cable from the motherboard right up to where it connects to the disks, cable again to the CDROM.

    So, IMO, there's no reason it can't be a ribbon, except for the convenience of crimping connectors wherever you want.

  • Ummmm.... (Score:3, Informative)

    by psyconaut ( 228947 ) on Sunday March 09, 2003 @08:30PM (#5473608)
    SCSI is already at "SCSI320"....which is 320Mbyte/sec NOT 320Mbits/sec!!!!

    That's already ~2.5Gbits/sec.

    And isn't there a SCSI640 working group, too?

  • by berwyn ( 409396 ) on Sunday March 09, 2003 @08:38PM (#5473633)
    There is a good article here 03 -03-03.asp?article_id=211

    The article states that the SAS drives won't work on a SATA channel, but SATA drive will on the SAS.

    I wonder if mobo makers like ASUS, ABIT, MSI and the likes will choose to have SAS ships on the mobo instead of SATA, as a performance feature?

    Lets hope so it would sure open a lot of option for upgrading a PC over time.
  • by dmadole ( 528015 ) on Sunday March 09, 2003 @08:59PM (#5473703)
    FYI - signals do not travel at the speed of light. Somewhere around 50-60% the speed of light in most types of cable.

    Overcoming the differences in arrival time of signals in a parallel cable is not significantly more difficult than handling clocking (and maybe clock recovery) and buffering and serial-to-parallel conversion on a serial interface.

    The main reason that parallel interfaces were popular years ago when things like SCSI were established was the electronics at the time just weren't very fast. The 74LS00 family logic that SCSI and parallel printer ports were designed around had a maximum clock rate of about 30Mhz. Add in margin for cable noise and distortion and 5-10Mhz was absolutely the most you could manage through any distance. So, if that wasn't fast enough for what you wanted to do, you used more wires in parallel.

    These days, it's relatively easy to put multi-gigahertz logic onto chips, and the fewer wires in a cable and connector, the cheaper, so serial wins.
  • by Anonymous Coward on Sunday March 09, 2003 @09:04PM (#5473718)
    IEEE1394 is a memory transaction based while SCSI is packet based.
  • Re:bits vs. bytes (Score:3, Informative)

    by g4dget ( 579145 ) on Sunday March 09, 2003 @10:31PM (#5474109)
    You don't need 10 controllers; the bandwidth limit is merely an electrical limit on the wire and connector, not on the controller. A single high performance USB2 or FireWire controllers should be able to do full USB2 or FW bandwidth per connector. Think of it like an Ethernet switch. In the past, a 100Mbps limit was aggregate, but now, the switch can do 100Mbps per port.

    You can already get USB2 and FireWire cards that can do high speed transfers simultaneously on several connectors, and if this really takes off, there is no reason why you couldn't have a card with 8 or 16 independent channels (ultimately, of course, it gets silly because PCI can't keep up anymore).

  • SATA vs SASCSI (Score:5, Informative)

    by Gerry Gleason ( 609985 ) <gerry@gerUMLAUTa ... .com minus punct> on Sunday March 09, 2003 @11:34PM (#5474386)
    The links with the story didn't have much info, but Google provides this one that has a technical slide presentation (PDF) that give more detail. It seems that the main 'compatibility' at the start will be identical cabling specs. They expect that mid-range host adapters would have both protocols, but PC chipsets would probably be SATA only and you would need a separate SAS HBA. It wouldn't surprise me if dual protocol PC chipsets arive at some point.

    One detail is that SAS is now point to point, just like SATA, and not a bus, but they also indicate that there would be boxes to split a single connection to a bunch of devices, sort of like network hubs. The protocol addresses 128 devices. It isn't clear whether a hub could have SATA devices hooked to it, or if that would require 1 serial channel per device from the host adapter. That is what I understood to be the case for SATA (need one port for each device, no hubs or sharing). The most important protocol difference should be that SAS is still multipoint, even if the connections are point-to-point, so both hosts and adapters need to arbitrate for the bus, while SATA hosts adapters just send out commands and data and wait for the drive to respond on the reverse channel.

    It wouldn't surprise me if devices eventually just supported both protocols, and maybe even auto-sensed the type of adapter on the other end. By the time these interfaces get common, I expect the cost differences to be negligible, so It begs the question of why SATA would survive. Because the cost differences are going to be sunk into the chipset designs with almost no marginal cost differences, both system and drive makers will probably save more by reducing the size of their product lines by having one product for both.

  • Re:Mbit != MByte (Score:1, Informative)

    by Anonymous Coward on Monday March 10, 2003 @12:53AM (#5474686)
    SATA and SSCSI compatiblity? F***ing duh! What do you think ATAPI is? The SCSI command protocol moving in packets across an IDE physical interface.

    If you bothered to read the second article you'd know that SATA and SSCSI will have compatable physical interfaces, no adapter needed. Who cares if ATAPI is SCSI over a IDE physical interface if i can't plug one into the other without spending more money for a adapter of some sort. Plus if you checked out the specs you'd know that SSCSI is going to be faster than both fibre channel and firewire, niether of which have the physical interface compatability of SSCSI with SATA. next time RTFA.
  • by AbRASiON ( 589899 ) on Monday March 10, 2003 @02:02AM (#5474863) Journal
    Contrary to popular beleif the SATA cables are approx 1mm thick, 6-7.5mm wide and quite "awkward" to work with :(

    I for one will be doing my best to hunt down a supplier which makes precise lengths so I can have mine cut to size as they aren't as easy to route as a ribbon cable (seriously!)

    Plus if you have 6 devices that's SIX cables in the box instead of 3,... - one of the small shortcomings of SATa :(

    (when I first heard about it, I was under the impression it dasiy chained with an "in" and an "out" port - boy did I think that was FANTASTIC... but I was sorely disapointed when I discovered I was incorrect) :(

  • Re:bits vs. bytes (Score:1, Informative)

    by Anonymous Coward on Monday March 10, 2003 @04:51AM (#5475342)
    But you're confusing the issue. You would need 10 controllers with the current IDE implementation.

    SATA, etc. is different, but that's neither here nor there since you're talking about the current implementation - okay, some bizaaro implementation that would require all-new silicon on both drive & controller for all these extra connectors.

    BTW, ultimately on an intelligent bus, you can do drive->controller->drive transfers without involving the CPUPCI bus. If SATA is implemented like regular ATA then yes, the PCI bus is going to get saturated (Intel works very hard to hobble standards so they're CPU-bound as much as possible, thereby increasing sales of high-end CPUs).

Thus spake the master programmer: "Time for you to leave." -- Geoffrey James, "The Tao of Programming"