Quantum 6-01376-05 User Manual

StorNext File System Tuning

The Metadata Controller System

StorNext File System Tuning Guide

• Zr: Hole in file was zeroed

Both traces also report file offset, I/O size, latency (mics), and inode

number.
Sample use cases:

• Verify that I/O properties are as expected.

You can use the VFS trace to ensure that the displayed properties are

consistent with expectations, such as being well formed; buffered

versus DMA; shared/non-shared; or I/O size. If a small I/O is being

performed DMA, performance will be poor. If DMA I/O is not well

formed, it requires an extra data copy and may even be broken into

small chunks. Zeroing holes in files has a performance impact.

• Determine if metadata operations are impacting performance.

If VFS throughput is inconsistent or significantly less than Device

throughput, it might be caused by metadata operations. In that case,

it would be useful to display “fsmtoken,” “fsmvnops,” and

“fsmdmig” traces in addition to “perf.”

• Identify disk performance issues.

If Device throughput is inconsistent or less than expected, it might

indicate a slow disk in a stripe group, or that RAID tuning is

necessary.

• Identify file fragmentation.

If the extent count “exts” is high, it might indicate a fragmentation

problem.This causes the device I/Os to be broken into smaller

chunks, which can significantly impact throughput.

• Identify read/modify/write condition.

If buffered VFS writes are causing Device reads, it might be beneficial

to match I/O request size to a multiple of the “cachebufsize” (default

64KB; see

mount_cvfs

man page). Another way to avoid this is by

truncating the file before writing.

The cvadmin command includes a latency-test utility for measuring the

latency between an FSM and one or more SNFS clients. This utility causes

small messages to be exchanged between the FSM and clients as quickly

as possible for a brief period of time, and reports the average time it took

for each message to receive a response.