Re: Improving IOPS

Gandalf Corvotempesta <gandalf.corvotempesta@xxxxxxxxx> · Sun, 6 Nov 2016 10:24:25 +0100



    Il 06/11/2016 03:37, David Gossage ha scritto:

    
          The only thing you gain with raidz1 I
            think is maybe more usable space. Performance in general
            will not be as good, and whether the vdev is mirrored or z1
            neither can survive 2 drives failing.  In most cases the z10
            will rebuild faster with less impact during rebuild. If you
            are already using gluster 3 node replicate as VM practices
            suggest then you are already pretty well protected if you
            lose the wrong 2 drives as well.

          
    Ok, i'll try again. I'm not talking about a single RAIDZ1
    for the whole server.

    
    Let's assume a 12 disks server. 4TB each. Raw space = 4TB*12 = 48TB

    
    You can do one of the following:

    1) a single RAIDZ10, using all disks, made up by 6 RAIDZ1
    mirrors. usable space=4TB*6 = 24TB

    2) 6 RAIDZ1 mirrors. usable space=4TB*6 = 24TB

    
    You'll get the same usable space for both solution.

    
    Now you have gluster, so you have at least 2 more servers in
    "identical" configuration.

    
    With solution 1, you can loose only 1 disk for each pair. If you
    loose 2 disks from the same pair, you loose the whole RAIDZ10 and
    you have

    to heal 24TB from the network.

    
    With solution 2, you can loose the same number of disks, but if you
    loose 1 mirror at once, you only have to heal that mirror from the
    network, only 4TB.

    
    * IOPS should be the same, as Gluster will 'aggragate' each pair in
    a single volume, like a RAID10 does, but you get much more speed
    during an healing.

    * Resilvering time is the same, as ZFS has to resilver only the
    failed disk with both solutions.

    
    What i'm saying is to skip the "RAID0" part and use gluster as
    aggragator. Is much more secure and faster to recover in case of
    multiple failures.

  
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