Re: long blocking with writes on rbds

Lionel Bouton <lionel+ceph@xxxxxxxxxxx> · Fri, 10 Apr 2015 16:10:43 +0200



    On 04/10/15 15:41, Jeff Epstein wrote:

    
      [...]

      This seems highly unlikely. We get very good performance without
      ceph. Requisitioning and manupulating block devices through LVM
      happens instantaneously. We expect that ceph will be a bit slower
      by its distributed nature, but we've seen operations block for up
      to an hour, which is clearly behind the pale. Furthermore, as the
      performance measure I posted show, read/write speed is not the
      bottleneck: ceph is simply waiting.

      
      So, does anyone else have any ideas why mkfs (and other
      operations) takes so long?

    
    As your use case is pretty unique and clearly not something Ceph was
    optimized for, if I were you I'd switch to a single pool with the
    appropriate number of pgs based on your pool size (replication) and
    the number of OSD you use (you should target 100 pgs/OSD to be in
    what seems the sweet spot) and create/delete rbd instead of the
    whole pool. You would be in "known territory" and any remaining
    performance problem would be easier to debug.

    
    Best regards,

    
    Lionel Bouton

  
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