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My storage needs are beginning to grow dramatically, and I was wondering how I could set up a raid. I'm currently planning on building a file server that is a ...
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  1. #1
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    Creating a hot-swappable file server.


    My storage needs are beginning to grow dramatically, and I was wondering how I could set up a raid. I'm currently planning on building a file server that is a RAID 5 server, so as to have some amount of redundancy.

    I've got multiple questions regarding building this server.
    1. Do I need five drives to begin with, or can I just convert everything to RAID 5, once I hit 3 drives without losing all my data.
    2. Will I be able to add more drives to my RAID 5 setup without losing all the data already on the drives.
    3. Do all the drives need to have the same RPM?
    4. Regarding the hot-swappable drives thing. Does this mean that I can use slots like I would an external hard drive? Plus in a drive, and it recognizes it on my machine?
    5. Has anyone ever used FreeNAS to build a fileserver of this sort? Can you tell me how difficult you found FreeNAS to configure? I plan to move over to CoreNAS when it comes out. Will I need to reformat all my drives if I do?


    Oh if it helps any, I plan to use a hardware RAID controller with this.

    Thanks a lot.

    Vamega

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    1. You don't need 5 drives, you need a minimum of 3 drives to have N+1 redundancy. I would suggest getting as many drives as you think you'll need, as expanding the array later on will be challenging.

    2. Probably not - you would need to take an image of the existing data, build a new larger RAID5 array and restore the data from the image.

    3. Having identical drives is always adviseable in RAID arrays. If the size or speed is different, the other drives usually default to the slowest or lowest capacity. I'd recommend 1TB enterprise class SATA disks, as they are excellent "bang for your buck" price wise, as well as having good platter density.

    4. It will depend on the hardware you house the array in - features like ths are usually the preserve of dedicatged NAS hardware. Typically it will mean you have to open the case and swap the faulty drive out - not always easy or safe whilst the box is running.

    5. I haven't used FreeNAS before, but I have used OpenFiler which does fairly similar things, and seems to do a good job.

    If your budget will allow it, I recommend teaming 2 x NICs into a switch that will support 9000k jumbo frames, and presenting your storage to your hosts as either iSCSI or NFS. Eg. setup a dedicated 'storage' ethernet network, don't just connect it to your LAN or the 1500 MTU will cause a bottleneck and high processor usage.


    Any questions, post here and I'll do my best to help.

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    There are hot swappable cages available for very reasonable prices. IcyDock is one manufacturer and Chenbro is another. Both are available at Newegg. This forum will not let me post a URL for you. Chenbro is good if you are buying a case along with the cage. If you have a case IcyDock is probably better for a retrofit. There are things you should do to disable the drive before removing it and to scan for the replacement. I would have given you a link but I still can't put links into this forum. They may not be needed with the latest kernels.

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  5. #4
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    Quote Originally Posted by vamega View Post
    1. Do I need five drives to begin with, or can I just convert everything to RAID 5, once I hit 3 drives without losing all my data.
    Actually, with Linux' software md-raid implementation, you can actually build a RAID5 array with only two drives, effectively mirroring the data.
    Quote Originally Posted by vamega View Post
    1. Will I be able to add more drives to my RAID 5 setup without losing all the data already on the drives.
    The advantage of choosing RAID5 when using only two drives is that you can easily 'grow' your RAID5 set with a third drive to gain more storage space. And once you run out of space, you can again 'grow' your RAID set with an extra drive.
    Although it is perfectly possible to grow a RAID-set to many drives, in practice you shouldn't go over 8 drives in a single RAID-set.
    Also you may consider using RAID6 if you use many drives. Where in a RAID5 set any one drive is allowed to fail, in RAID6 two drives can fail without loosing your data.
    Quote Originally Posted by vamega View Post
    1. Do all the drives need to have the same RPM?
    Technically no, but a RAID-array works best when all drives in it have more or less same performance. So if possible use the same drives across a array.
    Quote Originally Posted by vamega View Post
    1. Regarding the hot-swappable drives thing. Does this mean that I can use slots like I would an external hard drive? Plus in a drive, and it recognizes it on my machine?
    Don't know. As I personally am just in need of a lot of space and not so much in need for speed, I built my RAID-array on USB. This works fine for me and hot swapping works because USB works. I use software (mdraid) which does need two commands, one to fail a drive and one to add a new drive. eSATA should work equally well, although I am not sure if eSATA supports hot swapping (I think it does).
    Quote Originally Posted by vamega View Post
    I plan to use a hardware RAID controller with this.
    I personally don't like using hardware RAID because it needs hardware drivers that may not be available for Linux; because you introduce a single point of failure (the RAID interface); the format on the drives itself is proprietary and therefore if you loose your interface/drivers the data on the drives is gone too.

    Notice that not any RAID-level will protect you from user error, eg. deleting files ; RAID on it's own is not a backup scenario.

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    Notice that my arguments are pretty much Linux mdraid based. Other RAID solutions may have different properties.

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