Apple Xsan 1.x - Manual (Page 15)

Chapter 1 Setup and Tuning Guidelines 15
About SAN Write Latency
The waiting period from the time of the write request until the notification that the
request has been processed is called “latency,” and is an important measure of volume
performance. Xsan constantly monitors file system write latency and records hourly
summaries in the cvlog log file.
In general, peak metadata throughput begins to suffer when the average latency
exceeds 500 microseconds.
Xsan writes hourly summaries of metadata write latency into each volume’s log file.
Scan the log for entries that contain the text “PIO HiPriWr SUMMARY”.
To check file system metadata write latency:
m Open Xsan Admin, select the volume in the SAN Components list, and click Logs.
Choose Volume Log from the Show pop-up menu and the controller you want to
examine from the On pop-up menu. Then type PIO in the filter field and press Return.
The entry lists the average, minimum, and maximum metadata write latencies (in
microseconds) for the reporting period. For example:
[0802 15:20:30] (Debug) PIO HiPriWr SUMMARY LUN0 sysavg/350 sysmin/333
sysmax/367
To generate a new latency summary:
You can use the command line to generate a new latency summary on demand
instead of waiting for the next hourly update.
m Open Terminal and type
$ sudo cvadmin -F volume -e ‘debug 0x01000000’
where volume is the name of the volume.
To see the new summary entry from the command line, type
$ tail -100 /Library/Filesystems/Xsan/data/volume/log/cvlog