Discussion in 'Dell' started by Will, Feb 22, 2004.

  1. Will

    Leythos Guest

    I agree - RAID on the motherboard with no cache is a bad thing. In most
    cases they implemented a cheap RAID chipset and without the cache it's
    not much better than an OS RAID, but it does offer performance benefits.

    Most people don't understand RAID, they think that RAID is always faster
    than non-RAID, and that's just not always true. RAID 1 is almost as fast
    as a single drive for writes, but, can be faster than a single drive for
    reads since the data can be read from either drive. RAID 5 has poor
    write times, but great read times....

    In most cases, for home users, and for people doing PS type work, a
    simple MIRROR will save their butts in case of a hardware failure, but
    that's about the only benefit - most of these users set the mirror up as
    one large mirror, then partition it, and still think it's two drives for
    purposes of swap/temp space... They should have installed a single drive
    as a drive for swap/temp space and then they would have seen a
    Leythos, Feb 26, 2004
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  2. Will

    Leythos Guest

    RAID 1 is a mirror - two drives hold EXACTLY the same information. While
    you have twice the chance for a drive to fail, you only have half the
    chance for data loss due to failure of any drive. In the real world that
    means that loosing a single drive does not impact the user.

    RAID 0 is a stripe across two disks - this provides twice the chance for
    mechanical failure and twice the chance to loose everything in the event
    of a mechanical failure. Loosing either drive results in the complete
    loss of everything.

    RAID 5 is a stripe across 3+ disks with a parity stripe used to rebuild
    the other drives in the event of a failure. In this situation you can
    tipple your chance for a mechanical failure, but you benefit from being
    able to replace the defective drive and rebuild the entire array without
    the loss of data. During the time a drive is lost, you will notice a
    significant performance hit.

    Mechanical failure does not always mean data loss - only RAID 0 in the
    example above suffers from data loss.
    Leythos, Feb 26, 2004
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  3. Will

    Rob Guest

    I always mix up the two, that is the designation of RAID 0 and 1.

    Thanks for the lesson but I run RAID 0, 1, 5 across my network in both
    S/W and H/W implementations using Mylex, IBM, Adaptec and Promise cards.

    Rob, Feb 26, 2004
  4. Will

    Leythos Guest

    Rob - out of curiosity, what are you using RAID 0 for?
    Leythos, Feb 26, 2004
  5. Will

    Miro Guest

    Really, what happens if you blow two drives in a raid 5 setup ? Dont say it
    never happens, it did.
    Miro, Feb 26, 2004
  6. Will

    Miro Guest

    A mirror file is fine for storage but totally useless for a swap file. I
    dont think that PS is a special example of RAID useage for storage - I think
    somewhere back at the top someone was asking for a RAID that would improve
    speed not storage.

    The only setup that can improve swap file speed is a RAID 0 combo.

    Silicon Graphics has the worlds benchmark on RAID performance. Why do you
    think that is ?
    Miro, Feb 26, 2004
  7. Will

    Rob Guest

    My power work-station OS and apps drive, it's backed up after each
    install and my profiles and all other data reside on a server which has
    RAID 1 and 5 arrays.

    Rob, Feb 26, 2004
  8. Will

    Unknown Guest

    I'm still confused about those RAID answers. Why the hell cant you use a
    simple raid setup to have yet another HD attached to a computer and that HD
    simply for backups? Eg, similar to having a Master on primary and a Master
    on Secondary off the motherboard. Thus, if C screws up and as you have been
    good people and done backups all the time, just attach raid drive to primary
    or secondary port, boot off Drive Image 7 CD (just for example, not that I
    am pushing the program) and restore. Buggered if I know why a suddenly
    scrambled C drive that wasn't scrambled because of a hardware fault would
    affect a raid mounted HD as suggested above.
    Unknown, Feb 26, 2004
  9. Will

    Andrew Mc Guest

    You replace the drives in question and restore from last nights backup.
    Andrew Mc, Feb 26, 2004
  10. Will

    Miro Guest

    I once spoke to a very sad IT manager. He had a mirror setup for his boot
    drive. When the main drive started to wig out and write garbage the RAID
    controller obliged by writing garbage to the mirror. Thus killing both boot

    The magical assumption that a hard drive just dies isnt valid. It can do
    some very strange things in the read/write cycle and cause no end of bother
    on the data bus. Having said that, some software, such as databases also
    likes to write pre-and post- cache files which require a stable read-write
    cycle to marry up data changes. You can join the dots on the rest.
    Miro, Feb 27, 2004
  11. Will

    Miro Guest

    You have a means of backing up 2 terrabytes ? The answer is to use a "cold"
    standby in a spare drive bay. A drive that isnt running, spins up and takes
    the place of the first dead one. The second failure, if it is more than 30
    minutes after the first one, wont affect the raid stripe.

    RAID is supposed to be N-1 ( for every 5 drives you use, you only get the
    benefit of 4 drives storage in total.) but it is really N-2 or N-3

    I agree with the earlier post .... the Raptor is a drive to keep an eye on.
    Miro, Feb 27, 2004
  12. Will

    Leythos Guest

    The same thing that happens if you blow one drive in a single drive
    system - you loose it all.

    What's your point?

    The likelyhood of blowing more than one drive at a time is slim, unless
    you don't have a UPS, but you wouldn't be all that money into a R5 array
    and then not buy a UPS would you?

    In almost 10 years of configuring R5 arrays on servers, RAID 0+1, RAID
    1, and RAID 1, I've only had one instance where I've ever lost more than
    1 drive at a time. I should help you a little, I did loose everything on
    a Mirror (RAID 1) array set once, but that was because I didn't break
    the mirror and wiped the drive 0 boot partition.
    Leythos, Feb 27, 2004
  13. Will

    Leythos Guest

    Your very sad IT manager was ill informed - the RAID controller controls
    what is WRITTEN to the drive, not the drive itself. Your statement that
    the drive started wigging out and corrupted the other drive is bogus.
    What happens is that the RAID controller goes bad and takes out both
    drives. I have seen RAID controllers go bad and take out all drives
    data, not the drives, just the data, but I've yet to see a bad drive
    take out the other drives.

    I think if you talk with IT managers around the country you'll find that
    they would rather have a MIRRORED OS Boot drive than not have one. Think
    about it, without a redundant drive you loose everything if the single
    drive dies - not the data on the other drives/arrays, but it takes time
    to rebuild the OS, reapply security settings, etc... With a mirror you
    just swap out the bad drive and you are still up and running, not even
    any down time in the case of SCSI or SATA based systems.

    As for your database comments, I've managed and designed MS SQL
    databases with sizes from 20gb to 750gb, with a current one expected to
    hit 1.2tb later this year. Write caching on the controller is not a
    problem for the drives, that why a good card will have a battery and
    NVRAM, the drives don't know anything, they are dumb devices, it's the
    controller that does all the work. Even the database doesn't know it's a
    RAID array, it only knows that there is a bus to pull/feed data from/to.
    Leythos, Feb 27, 2004
  14. Will

    Leythos Guest

    As someone else posted further down, in a case where you (not in this
    post) mentioned 1.2tb of data, you would ALWAYS have a hot spare that
    auto-inserts itself in place of any suspected bad drive.

    I think your questions have exceeded the scope of people using Photoshop
    on workstations.

    On a workstation, a single mirrored set of drives will provide increased
    read performance and a redundant element in the case of hardware

    A second drive set (or a third single drive) used for the SWAP, TEMP,
    and scratch disk would be an ideal setup and provide the most
    performance with Photoshop.
    Leythos, Feb 27, 2004
  15. Will

    Andrew Mc Guest

    If you don't have the means of backing up 2 terabytes, then you shouldn't be
    storing it. Unless of course your lovely system can withstand a fire or a flood,
    or some other disaster. Or the data really isn't that important anyway. If it
    is, then anyone not backing up such an amount of data is an idiot.
    Andrew Mc, Feb 27, 2004
  16. Will

    Unknown Guest

    It's pretty damned obvious why a real time 100% of the time backup would
    stuff up if you mirror C elsewhere and expect elsewhere to work continuously
    every single time when C fails.
    Rot. I have had that happen even to my own computer. Back when 20gig was a
    medium sized drive, I had 2 and C died in 6 weeks. By then 40gigs were about
    and I bought a 40gig for C drive and restored from backup. No problems. What
    I do is have the other drive as a backup drive only where mirror images are
    stored but as my data doesnt have to be correct to the nanosecond, I only do
    mirrors 2 times a week (auto). I have compressed images on that drive. HDs
    DO just die and saying they dont is just plain wrong.
    Sure. That goes back a long way. I remember old 5.25 drives where you write
    something to it and wait. The drive light had to go out then let 30 seconds
    pass and it would come on again for a few seconds and go out again. THEN you
    could remove the disk. Doing it before that ended in dead data. However,
    what you said doesnt have any relevance to the last sentence of what I
    posted above.
    Unknown, Feb 27, 2004
  17. Will

    Unknown Guest

    Even that isnt necessarily true. You would have to know whether the drive
    had come into a situation that it shouldnt have, causing damage elsewhere.
    Eg, throw a wrench in moving gears and strange thigns happen!
    It's called "The FZZZST Principle". Sometimes a drive dies in ways most
    people never ever get to personally see. However, it still doesnt really
    explain that sentence I posed in that other letter.
    Yeah that may well be true. I still keep thinking of the "virus that got in"
    being mirrored though! :)
    No, not necessarily. Even Powerquest sell Drive Image 7 in a version that
    allows hourly incremental backup. This is, in fact, my personal preference.
    Eg, 9AM tomorrow morning the incremental gets done and at 9:30AM a virus
    gets in and wipes all the much needed data. What the company has lost is 30
    minutes of work. Now depending on the company, that may not be a great loss.
    Even in companies that WOULD consider that a great loss in some areas, there
    are others where it wouldnt be.
    No, with a proper mirrored array, your C goes down and the mirror takes
    over. You fix C and put it back online and the other drive then becomes the
    backup again, all done without interrupting work flow. Of course this DOES
    depend on the nature of what caused C to die.
    Admittedly more than I have done!
    Unknown, Feb 27, 2004
  18. Will

    Unknown Guest

    Unknown, Feb 27, 2004
  19. Will

    Unknown Guest

    Unknown, Feb 27, 2004
  20. Will

    Miro Guest

    There is nothing in the world more bogus than a theory which flies in the
    face of experience. Please learn some manners before you insult your own
    self. You are far too stupid to be taken seriously by me.
    Miro, Feb 27, 2004
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