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Thread: what makes a SCSI drive so much more reliable than anything else?

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    HEXUS.timelord. Zak33's Avatar
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    what makes a SCSI drive so much more reliable than anything else?

    I've been SCSI for.....gawd.....a long time.

    SO far, I've only ever got second hand drives, and some really are quite old.

    None.....I mean NONE.,...has let me down.

    Reading David's thread on a "real" server, and knowing MY requirements in the next 6 months for a serious storage server (serious in reliability, not space) for my new house, brings me round to asking:

    WHY is a SCSI drive so much better built?

    What bearings go in them? What hardware? Why do they spend so much more time and eoffrt on the production? DO they, or is there something inherently wrong with PATA and SATA drives?

    Is it simply the quality of components? Is it a deeper thing than that?

    Anyone really know? I mean...REALLY know?

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    Prize winning member. rajagra's Avatar
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    I think they spend more time testing and refining the designs of SCSI drives. And they probably do more thorough batch testing on production runs, then destroy any marginal drives - or even entire batches? Then they charge more!
    I don't think SCSI drives are that much more reliable, though. At work we have to replace a handful of failed SCSI disks every day. Mind you, we have hella lot of servers in our datacentres. But I know better than to trust any one disk.
    RAID systems with hot-swap drives certainly are the way to go if you're serious about protecting data.
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    Build quality, component quality, design quality. They cost more for a reason you know. SCSI drives are built to last, they don't cut corners to save money where they might on a ATA drive.

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    SCSI drives are designed for environments where they're tightly packed together into arrays (things can get warm) and where they'll be on all the time.

    Your run of the mill ATA drive isn't expected to be in such conditions.
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    ok....good answers....but not what I meant. I kinda knew that !!

    WHAT IS BETTER?

    Magnetic bearings? Balance of platters?
    Motor quality?

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    I imagine an modern ATA disc would be fairly reliable if it had the data density of some of those SCSI drives. At the end of the day, there's probably not a great deal of difference in the components used, but ATA needs to be cheap, whereas they can charge what they like for SCSI, and put that money into chucking the marginal cases.

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    Quote Originally Posted by Zak33
    ok....good answers....but not what I meant. I kinda knew that !!

    WHAT IS BETTER?

    Magnetic bearings? Balance of platters?
    Motor quality?
    Yeah all of them.
    A lot of it's not rocket science, just fairly simple things like having the spindle supported at both ends (many IDE drives don't). SCSI also tends to be faster drives with small platters with much tighter tolerances on components so they have better balance and stability. SCSI will tend to have a more powerful and accurate voice coil for the actuator and a much stiffer actuator arm to allow fast seeks without problems. The lower data density also means the heads can hover slightly higher off the platters which helps avoid head crashes.

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    Vive le pants! directhex's Avatar
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    scsi is largely expensive as there are 7 patents which need to be licensed (at high cost) per drive

    you'll find there's a migration towards SATA from the big enterprise storage companies (i.e. sata drives in a scsi-connected array)

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    Quote Originally Posted by Butcher
    things like having the spindle supported at both ends (many IDE drives don't). SCSI also tends to be faster drives with small platters with much tighter tolerances on components so they have better balance and stability. SCSI will tend to have a more powerful and accurate voice coil for the actuator and a much stiffer actuator arm to allow fast seeks without problems. The lower data density also means the heads can hover slightly higher off the platters which helps avoid head crashes.
    oh mate....THAT is an answer

    Quote Originally Posted by Advice Trinity by Knoxville
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    When it comes down to it, there's no reason all the things that make SCSI drives "good" couldn't be applied to any other interface. Now that SATA has NCQ (a feature that made SCSI's server performance superior than PATA/SATA for many many years) I expect to see more movement on developing enterprise drives for SATA. currently SCSI is faster than SATA, but the different is not large (320 vs 300 MB/s).

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    Quote Originally Posted by Butcher
    When it comes down to it, there's no reason all the things that make SCSI drives "good" couldn't be applied to any other interface.
    which was why i was wondering why EIDE drives die (a fair bit) and SCSI dont seem to (much at all really)

    What is it they say? "Buy cheap..buy twice"

    Quote Originally Posted by Advice Trinity by Knoxville
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    DR
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    I have never seen a SCSI drive fail in my lifetime - yet SATA/PATA I have seen DOA and drives which die after a period

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    Quote Originally Posted by David
    I have never seen a SCSI drive fail in my lifetime - yet SATA/PATA I have seen DOA and drives which die after a period
    I'll see your "never" and raise you a 10000rpm tea coaster I once had. Fujitsu 10krpm 9GB SCSI drive... one of the heads failed, according to the information I pulled out of the diagnostic software's log files.
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    DR
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    Did they RMA and swap out without fail?

    We have used them in servers for years - recently we moved to SATA and it caused problems....

    .... I have some SCSI drives here I ran for years and they were fine

    .... infact, one of the first servers HEXUS had an hammered - is still running on those drives

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    SCSI drives do fail , but it woudl appear to be less frequent.

    but thats why you have hotswap RAID , to allow you to replace hardware on the fly and not loose anything.
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    Prize winning member. rajagra's Avatar
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    Quote Originally Posted by Kez
    I'll see your "never" and raise you a 10000rpm tea coaster I once had.
    I'll see your coaster, and raise you by approx 500 SCSI disks I've seen fail.

    SCSI ... disks ... DO ...fail!
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