Hardware RAID setup/upgrade

Discussion in 'OT Technology' started by dtfromep, Mar 25, 2006.

  1. dtfromep

    dtfromep New Member

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    Okay, I am pretty well versed in desktop & server systems, but have never run into this before.

    Say I have a drive that contains data and is currently a single drive. I would like to use a HW RAID controller to mirror that drive without losing the data. Can this be done on a HW raid, or will the act of configuring the raid array kill the partitions/data?

    If nobody knows, I guess I can test this when the drive shows up and post up about it.

    Thanks,
    DT
     
  2. ShapeShifterz

    ShapeShifterz Longtime Lurker

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    This is possible. Setup your existing drive into a degraded array. This is obviously hardware dependent, but the dell percs can do it. As soon as you add a new disk, the array rebuilds itself.
     
  3. P07r0457

    P07r0457 New Member

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    the answer is that it depends on the controller. Some allow a non-descructive creation of a RAID 1 array (using one drive as the source) and some do not.
     
  4. dtfromep

    dtfromep New Member

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    Thanks for the insight. This would be on a home PC using the onboard raid controller for an MSI K8N Neo Plat. (NF250gb chipset). It is pretty basic, but it might allow for something like this to take place.

    Otherwise, I am off to get a decent raid card.
     
  5. Peyomp

    Peyomp New Member

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    If your controller can't do this, then use windows software raid. This is easy using software raid in windows or on Linux. And... its free.

    If you're using Win XP Pro, there is a hack to get this 'server only' functionality out of it.
     
  6. P07r0457

    P07r0457 New Member

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    software raid... eww
     
  7. Peyomp

    Peyomp New Member

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    Newsflash: all but the highest end RAID cards are software RAID in a vendor supplied driver. ;) AKA Less reliable than OS Software RAID. They're just IDE/SATA controllers with a RAID driver. There is no hardware RAID processing unless you pay $500 or more.
     
  8. P07r0457

    P07r0457 New Member

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    where did I say I use the crappy Promise (or anything similar) controllers?
     
  9. crontab

    crontab (uid = 0)

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    what hw controller are you using? is this a scsi card that goes into a box? or an external controller in a SAN? If this is a SAN then you may not be able to do it since some are picky about what disks are used.

    what you need to do is encapsulate that disk prior to making is a single member mirror. Put it in the controllers group.

    worse comes to worse you can just plop in the controller, extra disks, build a mirror, and copy that data from the single disk to the mirror set over night.
     
  10. Peyomp

    Peyomp New Member

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    He's using a low end IDE card. Better to use softare RAID. You can easily build a mirror in XP, 2K, 2003 the Linux.
     
  11. deusexaethera

    deusexaethera OT Supporter

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    Software raid is so slow! Why would anybody use it?

    Another option, if you want to do more than RAID 1, is to hook up all but one of the new drives into the RAID controller, configure them as degraded, ghost your old drive onto the new degraded array, and then tell the RAID controller that the old drive is now the replacement for the 'failed' drive in the array.

    The one time I did this, I had to actually configure the old drive as an active member of the new array, save the config, and bail out of the RAID software before it tried to initialize the new array. Then I connected the old drive to a different cable and ghosted it onto the new array before plugging it back into the RAID controller as a permanent member of the new array.

    Use at your own risk.
     
  12. Peyomp

    Peyomp New Member

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    Actually software RAID compares favorably with the RAID-in-driver cards that 95% of the IDE/SATA stuff is.
     
  13. P07r0457

    P07r0457 New Member

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    peyomp, now you're being the troll.... take a hike.
     
  14. Peyomp

    Peyomp New Member

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    Now you're being an asshat. Take a walk.

    Because what I said is factual, verifiable and true. If you want to attempt to participate, then do so with facts. I'm just trying to give good advice. Troll elsewhere.
     
    Last edited: Mar 30, 2006
  15. deusexaethera

    deusexaethera OT Supporter

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    (insert random, unhelpful trolling comment here)
     
  16. deusexaethera

    deusexaethera OT Supporter

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    All joking aside, and in the interest of not actually being a troll, I shall now explain my distaste for software RAID.

    1. Performing the RAID calculations (even for RAID 1, which is a simple "does byte A == byte B?" calculation, as opposed to the XOR calculations needed for other RAID levels) in a general-purpose chip instead of a dedicated chip is much less efficient, and on top of that the calculations are being done in the same chip that all your other programs are running in, so the extra inefficiency impacts the speed that your programs can run at.

    2. Software RAID stores its configuration in the Windows Registry, which is a bad thing because the Registry is much more easily-corrupted than is an EEPROM chip connected to dedicated hardware. One good virus, or one bad Registry edit, and POOF goes your RAID and all the data on it.
     
  17. P07r0457

    P07r0457 New Member

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    as far as I know, most cheap "software-based" raid *controllers* (which do have their own dedicated hardware, but offload some tasks to the CPU and utilize main system memory) do still store their configuration on a dedicated EEPROM. Some exceptions are a few Asus boards that have an entirely-software-driven RAID5 implementation. However, I beleive that most promise and VIA RAID controllers, although still not dedicated RAID implementations, are certainly better than a strictly software-based solution.
     
  18. Peyomp

    Peyomp New Member

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    As of a couple years ago, every single IDE/ATA RAID card I looked at except for the top of the line $2K SATA RAID card from one manufacturer, did all its computation in the driver, had no memory of its own (critical for RAID 5 performance) and was essentially software RAID with NO custom RAID processor. Just a couple IDE controllers on a board with a driver.

    To me thats wasting money. Thats all I'm saying.
     
  19. P07r0457

    P07r0457 New Member

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    The Promise SX4 is easily under $175 and uses it's own dedicated SDRAM slot.

    Many other controllers, such as Adaptec, also have their own dedicated memory, and are under a few hundred.
     
  20. ShapeShifterz

    ShapeShifterz Longtime Lurker

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    I can't speak for every RAID controller out there, but I've done ~actual~ benchmarks on linux software raid vs a few LSI RAID controllers.

    In most cases, the linux software RAID outperformed the LSI adapters. Overall CPU usage wasn't even an issue.
     
  21. EvilSS

    EvilSS New Member

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    Might as well not even try then. Windows software RAIDs WILL fail. Not might, not maybe. The WILL fail. I'm glad you like them but if you've never spent half a night working with a disk editor to manually edit a broken software raid partition to recover the data on the drive then I'd suggest you give it a try before recommending it to anyone. It's a blast.

    There are plenty of consumer, hardware raid products out there for under $300 that will actually not loose all your data at some random future time.
     
  22. Peyomp

    Peyomp New Member

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    And I've had software RAID cards fuck up and all the data was lost. Those WILL fail too. How is the recovery process any different then? When a Software RAID 1 mirror fails, mount the good drive as a single disk, pop in a new drive, and re-mirror.
     
  23. EvilSS

    EvilSS New Member

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    What part of "hardware RAID products" did you interpret as software RAID card??

    OS RAID arrays tends to fail at the software level, not the drive (although replacing a failed drive on one is a crap-shoot in itself). I had a customer that used one under Windows 2000. A service pack install hosed it. Poof. Gone. Both drives were fine, all the data was there, but the upgrade had wonked up the partition. I spent most of the night with a disk editor putting the partition back together so they could get the data (which, of course, they didn't bother backing up) off.

    I have yet to see any Windows RAID last more than 2 years. Most fail within a year or less.
     
  24. Peyomp

    Peyomp New Member

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    I've run Linux mdadm software RAID for a year at a time without failulre.

    As to hardware RAID products, I don't believe the cards you mention have ASICs. I'd love to be proven wrong.
     
  25. EvilSS

    EvilSS New Member

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    I don't remember even mentioning a specific card, however all Promise cards have ASICs. Considering they MAKE the ASICs this should not be a surprise. You are probably confusing the ASIC with a dedicated I/O Processor. The Promise ASICs have hardware XOR but they offload some of the processing to the system CPU. For an all hardware card, the LSI MegaRAID SATA 150-4 has it: they use an Intel XScale processor. edit: for about $250 street.

    And I think you made my point. Your RAID arrays last for a YEAR at a time. I assume that is about when you rebuild the OS? I have a DL580 that I haven't updated the RAID configuration on in several years and it has never failed or required any additional maintenance even though I've reinstalled the OS numerous times. So,

    OS < Hardware Assisted < All Hardware.

    Sorry, but even the Promise cards are more reliable than the OS all-software RAID systems. All the cards have hardware error checking to prevent bad data and they will always keep the config, even if the OS tanks.
     

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