NFS Performance Issue

There was an issue found in Data ONTAP 7.2.3 and earlier where ONTAP would sometimes not release networking buffers fast enough, resulting in very poor performance. The main symptom of this issue can be seen by watching the output of "sysstat 1" over time and noting that the number of NFS ops will periodically drop to 0 for several seconds, and then resume normal activity.

Two other tell-tale signs are the "Total discards" and "No Buffers"
counters in the output of "ifstat -a". These are TCP or UDP packets that ONTAP had to discard because it did not have enough memory resources to handle them. If they are anything other than zero, there is a problem:

RECEIVE
Frames/second: 21600 | Bytes/second: 28641k | Errors/minute:
0
Discards/minute: 429 | Total frames: 1939k | Total bytes:
2564m
Total errors: 0 | Total discards: 486 | Multi/broadcast:
0
No buffers: 486 | Non-primary u/c: 0 | Tag drop:
0

You can read more about this BURT here:

http://now.netapp.com/NOW/cgi-bin/bol?Type=Detail&Display=226424

This issue has been fixed starting in Data ONTAP 7.2.4 and later.