Hi, we’ve aligned all our Vmware vmdk’s according to the Netapp best practices while tracking the pw.over_limit counter
see: http://www.vmadmin.info/2010/07/quantifying-vmdk-misalignment.html
Counters that indicate improper alignment ( ref: ftp://service.boulder.ibm.com/storage/isv/NS3593-0.pdf)
“There are various ways of determining if you do not have proper alignment. Using perfstat counters, under the wafl_susp section, “wp.partial_writes“, “pw.over_limit“, and “pw.async_read,“ are indicators of improper alignment. The “wp.partial write“ is the block counter of unaligned I/O. If more than a small number of partial writes happen, then IBM® System StorageTM N series with WAFL® (write anywhere file layout) will launch a background read. These are counted in “pw.async_read“; “pw.over_limit“ is the block counter of the writes waiting on disk reads.”
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So the pw.over_limit counter is still recording an 5 minute average of 14 with 7-10 peaks in the 50-100 range at certain times of the day.
If I look at the clients talking to the Netapp those times its mostly Oracle RAC servers with storage for data and voting disks on NFS.
This leads me to the question: What if any are the other possible sources for unaligned IO on Netapp?
All references I find are vmware vmdk – but are there others like Oracle which may be doing block IO over NFS?
Many thanks
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Fletcher Cocquyt
http://vmadmin.info
