Quantum 6-01376-05 User Manual

  StorNext File System Tuning

The Metadata Controller System

StorNext File System Tuning Guide

16

The latency-test command has the following syntax:

latency-test

 index-number [seconds]

latency-test

 all [seconds]

If an index-number is specified, the test is run between the currently-

selected FSM and the specified client. (Client index numbers are 

displayed by the cvadmin who command). If all is specified, the test is 

run against each client in turn.
The test is run for 2 seconds, unless a value for seconds is specified.
Here is a sample run:

snadmin (lsi) > latency-test

Test started on client 1 (bigsky-node2)... latency 55us

Test started on client 2 (k4)... latency 163us

There is no rule-of-thumb for “good” or “bad” latency values. Latency 

can be affected by CPU load or SNFS load on either system, by unrelated 

Ethernet traffic, or other factors. However, for otherwise idle systems, 

differences in latency between different systems can indicate differences 

in hardware performance. (In the example above, the difference is a 

Gigabit Ethernet and faster CPU versus a 100BaseT Ethernet and a slower 

CPU.) Differences in latency over time for the same system can indicate 

new hardware problems, such as a network interface going bad.
If a latency test has been run for a particular client, the cvadmin who 
long

 command includes the test results in its output, along with 

information about when the test was last run.

0

The following SNFS mount command settings are explained in greater 

detail in the 

 man page.

By default, the size of the buffer cache is 32MB and each buffer is 64K, so 

there is a total of 512 buffers. In general, increasing the size of the buffer 

cache will not improve performance for streaming reads and writes. 

However, a large cache helps greatly in cases of multiple concurrent 

streams, and where files are being written and subsequently read. Buffer 

cache size is adjusted with the buffercachemin and buffercachemax 

settings.