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  1. #1

    Question How to share the harddisk array for two servers?

    We're planning to run load balancing on new servers (we're running SCSI), but there's a question,

    1) Can we share the harddisk array from server A to server B? using the external connector from SCSI raid card?

    2) When a server is crashed, can another server still able to access the harddisk array?

  2. #2
    Join Date
    Jan 2003
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    While the answer is 'yes' it comes with some serious caveats. You can hook the servers together over the SCSI bus, but often the servers will place different voltages on the lines and cause trouble. SCSI over Fibre Channel or iSCSI will work around that, though.

    The second hurtle is making sure both servers see each other's changes, since modern OSes cache all their writes. Unless you have a filesystem designed for the task (GFS is one), you will corrupt your filesystem and data into total gibberish.

    Your concept can work, but a central file server is usually a better solution until you're ready for a full-blown SAN.
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  3. #3
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    i think he meant same disk array but not the same disks on that array?

    i saw that on some setups, it relly depend on the hardware though.
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  4. #4
    We're using the same hardware on both servers, so there wouldn't be a voltages problem?

    How about one SCSI disk for server A and one for server B, then run Raid 1 between 2 servers?

    Do we need iSCSI card and specificed filesystems to do that?
    Last edited by nowisph; 04-11-2004 at 03:01 AM.

  5. #5
    Originally posted by Bashar
    i think he meant same disk array but not the same disks on that array?

    i saw that on some setups, it relly depend on the hardware though.
    yea, the same disk array.

    Unfortunately the SCSI NAS/SAN solutions are too expensive to afford.

  6. #6
    Join Date
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    Why not get a dedicated machine to throw in the middle, and NFS mount shares on each webserver? I would create one OS disk for each server, and just have them nfs mount the "master" share. The company I work for hosts several sites load-balanced like this. One inparticular uses a Brocade Silkworm, but that's some serious drive balancing.

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  7. #7
    a file server is not stable as its OS is not redundant, when it goes down, 2 servers will be out of service, this is one-point-of-failure, and the cost is even higher than NAS solution.

    We would rather choose a mid-range NAS as it can be used for 4 servers without worrying about downtime.

    But as I mentioned the NAS equipment is expensive so we're considering load-balancing on 2 servers.

  8. #8
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    what is the difference between the nfs file server and the nas ?
    isn't the nas a standart server in a custom box usig a modded os ?

  9. #9
    major bands NAS are using hardware OS with redundant, not sure for other NAS from smaller bands.

  10. #10
    Join Date
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    Originally posted by netswitch
    what is the difference between the nfs file server and the nas ?
    isn't the nas a standart server in a custom box usig a modded os ?
    NAS would be a seperate network accessible storage device while using NFS mounts would enable you to keep the array in one machine and simply mount its partitions over the network.
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  11. #11
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    Doesn't NFSv4 support disconnected feature where it keeps a cached copy of data on the client side then merges the changes when the server is back online. I haven't used it yet but that feature does work well with OpenAFS.

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