Help: Software RAID 5 - Linux - Cheap

Discussion in 'OT Technology' started by [AWD] Major Dumps, Nov 26, 2006.

  1. [AWD] Major Dumps

    [AWD] Major Dumps ahhhh this is a good dump

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    So I'm planning on building a Fedora Core data server on software RAID 5 (if I can do it, otherwise I'm switching to ubuntu). But before I order parts, I have a couple questions:

    1.) Can I start with a single drive, install my linux, add drives later and create a RAID 5 array when I have enough drives in the computer? In other words, I want to add storage space later on and not have to format or lose any of the data to construct the array (ie. I will already have content on the drives when I move to make RAID 5)

    2.) Can it be done in fedora core?
     
  2. deusexaethera

    deusexaethera OT Supporter

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    It's my understanding that no operating system can be installed onto a software-controlled striped array, because the operating system won't know where to find its files until it's already loaded itself. That's what you call a paradox.

    Anyway, you don't want to use software RAID. It will eat massive amounts of CPU power. Go buy a cheap RAID card -- the NetCell cards are quite effective, and unlike other cheap RAID cards, they don't rely on the CPU to provide parity-checking.
     
  3. [AWD] Major Dumps

    [AWD] Major Dumps ahhhh this is a good dump

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    I'll just get a dedicated system drive then.

    also, how many drives will that card support? i plan on adding drives when funds and propensity become available. can i replace a drive with a larger one later on? do all the drives have to be congruent?
     
  4. crontab

    crontab (uid = 0)

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    1.) Depends on what you use. I assume you are using LVM2 so no. It doesn't preserve the data on any lun, plus you can't relayout from one type to another, in your case a JBOD's to RAID5. If you had an existing RAID5 set, then yes you can grow it, by adding another column.

    2.) Not out of the box, Logical Volume Manager 2 is not too dynamic. Veritas is a great 3rd party software package, but it's not free. It can do what you're looking to do and much more. The standard lic for the basic features of vxvm and vxfs is ~$3K per host.
     
  5. deusexaethera

    deusexaethera OT Supporter

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    It supports up to 5 drives. You can add more drives later and the card will give you the option to expand your current RAID or make a new RAID.

    With a hardware RAID card, the RAID functionality is provided by a device other than the CPU, and controlled by software other than the OS, so you can safely install the OS onto a hardware RAID. In fact, I have my home computer set up this way.

    The card will use the smallest available space on all of the disks connected in a single RAID -- that's the nature of the beast. You can swap bigger disks in place of smaller disks, but I'm not sure whether the card is smart enough to automatically expand the usable space on the disks when it realizes that all of the disks are bigger than they used to be. In any event, once the card is persuaded to expand the usable space on the disks, you'll still need something like PartitionMagic to enlarge the partitions on the RAID to fill the extra usable space.
     
  6. mobbarley

    mobbarley Active Member

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    You could have a sepearate system disk, use it as temporay storage. Then when you buy the RAID HDs, build the raid and move the files over.

    If its a dedicated computer, who cares?


    RAID card is easier to set up, but software raid is cheaper, take your pick. There are plenty of guides out there for both.
     
  7. [AWD] Major Dumps

    [AWD] Major Dumps ahhhh this is a good dump

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    which linux distros do you have software RAID experience for?
     
  8. deusexaethera

    deusexaethera OT Supporter

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    If I'm running a fileserver, I'd rather reserve the CPU power for automated defragmentation, error-scanning, and NTFS file compression. $100 for a simple RAID card offloads one more task from the CPU, making it that much easier to have a fully self-maintaining system, and with the NTFS file compression you can come close to doubling your storage capacity FOR FREE.

    Furthermore...if you use software RAID, you can't store the OS on the striped array, and you lose the protection that RAID is supposed to give. The OS hard drive can fail too, you know.
     
  9. [AWD] Major Dumps

    [AWD] Major Dumps ahhhh this is a good dump

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    i've given much thought to the subject, but i have decided to go with software. at this point, i'm interested in the software implementation.
     
  10. deusexaethera

    deusexaethera OT Supporter

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    Have fun learning, I guess. When you get serious, you'll want a RAID card though. Trust me, even a simple mirror array eats prodigious CPU power -- a striped array is a goddamn juggernaut if it's not managed by dedicated hardware.
     
  11. mobbarley

    mobbarley Active Member

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    I'm running mine on slackware. No real reason for that except that I have always used slackware & I know I can do a reasonably minimal install.

    to me the main advantage of software is that if your motherboard or IDE/SATA card dies you can replace it and keep the raid. If you have a promise card or whatever and two years down the track it dies and you cant find a replacement.... good bye data?
     
  12. mobbarley

    mobbarley Active Member

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    I use an intel STL2 mobo with 2x P3 1Gig, 1 gig ram. havent benchmarked it but it going from a 100 card to a 1000 card made a big speed difference so its well over 100Mb/s.

    edit: oh and 4x Segate PATA drives in raid 5 from 2x no name ide cards with sil chipsets. 2x ibm scsi drives in a mirror for system.
     
  13. Peyomp

    Peyomp New Member

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    I've done software RAID 1 on a root partition... creating software RAID arrays is an option as you install redhat/fedora. Its quite easy. As to booting, I think I might have booted off it, or there might be a /boot or something that is not RAID.
     
  14. deusexaethera

    deusexaethera OT Supporter

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    Meh...I don't like mirrors. Too inefficient. They don't do anything that striped parity can't do, and striped parity has lower data overhead. Of course, it also demands dedicated hardware to handle the parity calculations, but so what? If you're going to implement RAID, fucking do it right I say.
     
  15. mobbarley

    mobbarley Active Member

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