Monday, February 17, 2014

Reading LUN Stats -o

netapp1> lun stats -o
    /vol/UCvol/UClun  (98 days, 0 hours, 46 minutes, 51 seconds)
 Read(kbytes)  Write(kbytes)  ReadOps  WriteOps  OtherOps  QFulls  PartnerOps PartnerKBytes 
     15940415      640772      30487379  8734    9767    0     30442488       15496708 

A few things about this are not immediately intuitive.  First, statistics labeled "Partner" are indirect IO, passed through the cluster interconnect.  This means both heads have to process the information, which is adds up to considerable overhead in terms of work and latency.  

Second, the statistics not labeled  "Partner" are totals: they include both the direct and indirect IOPS.  At first glance you'd see that ReadOps is a very close number (.1% off) to PartnerOps, which would indicate that the traffic is being load balanced across indirect paths.  

But that would be counting the same Ops twice.  If you add up ReadOps, WriteOps, and OtherOps, that's the total number of direct and indirect Ops.  If you then subtract PartnerOps, that resulting number (63392 Ops) is the number of direct Ops.  That's .2% direct IOPS, which indicates a serious pathing configuration issue.

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