[9fans] Mirrorarenas in p9p - Plan9

This is a discussion on [9fans] Mirrorarenas in p9p - Plan9 ; I'm running a p9p venti server under Linux using several (small by current standards) physical drives as my arena pool. I got a 500GB external USB drive to use as a backup of the arenas. But here's the gotcha. The ...

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Thread: [9fans] Mirrorarenas in p9p

  1. [9fans] Mirrorarenas in p9p

    I'm running a p9p venti server under Linux using several
    (small by current standards) physical drives as my arena
    pool. I got a 500GB external USB drive to use as a backup
    of the arenas. But here's the gotcha. The number of blocks
    per cylinder on the 500GB drive isn't the same as the other
    smaller drives. So, I can't create a partition that's exactly
    the same size as one of the smaller drives, which means that
    the last arena is a different size when I format it. mirrorarenas
    complains about that and considers it fatal. I modified
    it so that if the destination arena is bigger than the source,
    it's just a warning and not fatal and it's happily mirroring
    as we speak. But I've got a couple of questions:
    - Is this going to cause any problems?
    - Is there a better way to handle this?

    Thanks,
    BLS



  2. Re: [9fans] Mirrorarenas in p9p

    > I'm running a p9p venti server under Linux using several
    > (small by current standards) physical drives as my arena
    > pool. I got a 500GB external USB drive to use as a backup
    > of the arenas. But here's the gotcha. The number of blocks
    > per cylinder on the 500GB drive isn't the same as the other
    > smaller drives. So, I can't create a partition that's exactly
    > the same size as one of the smaller drives, which means that
    > the last arena is a different size when I format it. mirrorarenas
    > complains about that and considers it fatal. I modified
    > it so that if the destination arena is bigger than the source,
    > it's just a warning and not fatal and it's happily mirroring
    > as we speak. But I've got a couple of questions:
    > - Is this going to cause any problems?
    > - Is there a better way to handle this?


    It would be best to set up an arena set that
    matches the one you are mirroring exactly.

    To cope with the lack of real partitioning
    support in operating systems that are not
    Plan 9, the p9p venti lets you specify disk
    subpieces in the partition names. So you
    can say /dev/hda:0-10G to get the first ten
    gigabytes of /dev/hda. Or /dev/hda:0-12345M
    or /dev/hda:1G-123123123123M etc.

    Also, if you do create a Plan 9 partition and
    then prep it to make subpartitions (you'd have
    to use 9vx, copying the binaries from sources),
    then p9p venti can handle those partition names
    too: /dev/sda1:arenas assuming /dev/sda1 is a
    Plan 9 fdisk partition containing a subpartition
    named arenas.

    Yes, it's terrible. You use Unix long enough,
    you get used to that.

    Russ



  3. Re: [9fans] Mirrorarenas in p9p

    > Also, if you do create a Plan 9 partition and
    > then prep it to make subpartitions (you'd have
    > to use 9vx, copying the binaries from sources),
    > then p9p venti can handle those partition names
    > too: /dev/sda1:arenas assuming /dev/sda1 is a
    > Plan 9 fdisk partition containing a subpartition
    > named arenas.


    So here's what I ended up with. I installed 9vx on
    the machine and used that to partition the big
    drive: one fairly big partition with 4 subpartitions
    for the 4 arena disks already on the machine. The
    p9p mirrorarenas didn't like the partition name
    notation. It calls initpart which calls parsepart
    which seems to only like the numeric range notation.
    But running the Plan 9 mirrorarenas in 9vx works
    just fine. So I'm pretty much where I want to be
    for now.

    Thanks,
    BLS



  4. Re: [9fans] Mirrorarenas in p9p

    >> Also, if you do create a Plan 9 partition and
    >> then prep it to make subpartitions (you'd have
    >> to use 9vx, copying the binaries from sources),
    >> then p9p venti can handle those partition names
    >> too: /dev/sda1:arenas assuming /dev/sda1 is a
    >> Plan 9 fdisk partition containing a subpartition
    >> named arenas.

    >
    > So here's what I ended up with. I installed 9vx on
    > the machine and used that to partition the big
    > drive: one fairly big partition with 4 subpartitions
    > for the 4 arena disks already on the machine. The
    > p9p mirrorarenas didn't like the partition name
    > notation. It calls initpart which calls parsepart
    > which seems to only like the numeric range notation.
    > But running the Plan 9 mirrorarenas in 9vx works
    > just fine. So I'm pretty much where I want to be
    > for now.


    It should be there as of HG revision 2825 (July 3).
    The particular file contents that I expect are at
    http://swtch.com/go/venti-plan9-partitions
    It's at the bottom of the file.

    In addition to /dev/sda1:arenas you can say
    /dev/sda:arenas -- the code parses the fdisk table
    to find the Plan 9 partition too (but it's also happy
    if you give it the Plan 9 partition directly).

    Using 9vx is fine, of course, but this is one less
    moving piece in your mirroring scripts.

    Russ



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