Without going too crazy into technical detail (statit counters), the easiest way has been to look at sysstat output: if disk reads are significantly higher than net out or tape backup (depending on the workload - ie, no reconstructs or reallocates running), then you could probably use minra.

That type of fingerprint signifies that the disks have more reads than necessary. Some are ok but too many will cause performance problems.

Beyond this, you can look at the statit and wafl_susp counters to determine things about disk fragmentation and I/O and readahead cache (respectively).

Glenn

-----Original Message----- From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of Peter D. Gray Sent: Thursday, August 31, 2006 1:59 AM To: toasters@mathworks.com Subject: when to use minra ?

Does anybody have recipes or suggestions on how to work out if turning on minra will improve or decrease performance? Are there counters you can query in ONTAP that are helpful?

Regards, pdg

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sts more data from the same file, the data is already in the cache so the response is faster.

However, if your file reading pattern is completely random, then minra off may result in extra disk reads that are wasted because the client never requests the extra data read from the disks. Your reading pattern may not be as random as you think, however, and it is very unusual for minra on to be helpful.

I have seen one situation where minra on was a win. On a FAS960c clustered pair and we had FC LUNs. The clients were Solaris boxes running Veritas. For performance we used Veritas to stripe a pair of LUNs, one LUN from each filer. We built a Veritas filesystem on the striped LUNs. As you can imagine, this thoroughly scrambled up file data because it was striped over two filers, somewhat defeating the Netapp read ahead strategy. We were storing email on this striped filesystem and so we had a very heavy read load. With minra off disk reads in KB/sec were about 10% to 20% higher than FC writes, indicating that the extra reads were probably going to waste. I turned minra on and the disk reads dropped to a little less than the FC writes.

We have since switched from FC LUNS to NFS mounted volumes and turned minra back off.

Steve Losen scl@virginia.edu phone: 434-924-0640

University of Virginia ITC Unix Support