I originally tried posting this back on April 11 - now that the list is "fixed" I want to try again - thanks:
Hi, we¹ve aligned all our Vmware vmdk¹s 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) ³There are various ways of determining if you do not have proper alignment. Using perfstat counters, under the wafl_susp section, ³wp.partial_writes³, ³pw.over_limit³, and ³pw.async_read,³ are indicators of improper alignment. The ³wp.partial write³ 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 ³pw.async_read³; ³pw.over_limit³ is the block counter of the writes waiting on disk reads.²
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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
