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Thread: Linux Software RAID help needed

  1. #1

    Linux Software RAID help needed

    Hi there. NooB here. I'm in the process of setting up a home server using ClarkConnect, which I gather is based on Redhat Linux. I've got a bunch of SATA hard drives I want to set up in a RAID array. I have an 80GB drive which is to be dedicated for the operating system and applications. 2 x 250GB drives and 2 x 500GB drives I want to configure in a RAID array using Linux software RAID.

    I'm trying to work out the best configuration of these drives in an array. I'm thinking of a striped RAID0 config between the 2 x 250GB drives. I was wondering, is it possible to use that RAID0 striped array (total 500GB) can then be used with the 2 x 500GB drives in a RAID5 configuration so I end up with 1TB of storage in a RAID5 array? I've read a bit about LVM and I'm trying to understand if this would help me in some way if I combined the 2 x 250GB drives.

    Any help would be appreciated. I'm kinda stuck. I just can't seem to find any info on a similar config. It seems it should be possible but I just have no idea.

  2. #2

    First, that's a lot of storage! wow!

    Second, software raid and LVM are different subjects. Are you using all of this for Linux ( Clark connect or Red Hat)? If I were using it all for linux, I would install alllllllllll that storage. You would have a /dev/hda (applications) /dev/hdb /dev/hdc (250GB) /dev/hdd /dev/hde (500GB). Did I get that right?

    #fdisk /dev/hdx
    m - (help)
    1. n - new
    2. p - primary partition
    3. 1 - /dev/hdx1
    4. (default starting cylinder) size: +2500MB (or +5000MB)
    5. t - set partition type
    6. fd - RAID
    7. w - write and exit
    8. #partprobe

    ***Do the same thing for /dev/hdb /dev/hdc /dev/hddd /dev/hde
    # mdadm -C /dev/md0 -l 5 -n3 -x1 /dev/hdb1 /dev/hdc1 /dev/hdd1 /dev/hde1
    #mkdir /mnt/raid
    #mkfs.ext3 /dev/md0
    #mount /dev/md0 /mnt/raid
    #vi /etc/fstab
    /dev/md0 /mnt/raid ext3 defaults 0 0

    Let me know if that works, I've never done this in your situation before.

    For LVM. Use commands lgcreate, vgcreate, and lvcreate. (that goes in more depth)


  3. #3
    Hiya Josh. Thanks for your reply. In answer to your questions:

    1. Yes, this is all for Linux. It'll be the basis for my home network file server. 2. Yes, you've got it right wrt the drives. 80GB main drive for apps, 2 x 250GB plus 2 x 500GB drives for file storage.

    I'm not at home yet to wade through your script. Given that I'm a complete noob at Linux, I don't even know what other questions to ask right now. I'm assuming that you think my idea will work? That is, to stripe the 2 x 250GB drives and use them as part of a RAID 5 array with the 500GB drives? So I guess you are giving me the commands to set that up?

    I have a lot to learn.


  4. #4
    If you're not certain you need all that space, I'd say go RAID 1. Unless you plan on using every last byte, the fault tolerance can really come in handy (if you have 4 drives striped, you lose everything if one fails, and I don't know how that setup would handle RAID 4 or 5, you'll probably lose a lot of space and may be around the same space as RAID 1 anyway).
    63,000 bugs in the code, 63,000 bugs,
    ya get 1 whacked with a service pack,
    now there's 63,005 bugs in the code!!

  5. #5
    Hmm, you might be right, countach. I've been doing some further reading. Every reference I've seen seems to indicate that in a RAID 5 config, you will only ever get (smallest disk capacity)*(# drives) - (smallest disk capacity) of storage. So effectively with my setup, I may as well go RAID 1 because I end up with the same number. No mention of my RAID 0 on two drives then a RAID 5 config with two bigger drives. Looks like back to the drawing board.

    Thanks for the input guys.

  6. #6
    Good Guru
    Schotty's Avatar
    Join Date
    Jul 2001
    Milwaukee, WI
    Could try two lvm groups, one main, one backup. lvm is a cakewalk to expand - adding or removing volumes is a simple ejection or addition away, unlike raid.

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