Lustre 1.6 Operations Manual

20.2.3 Client Read-Write Offset Survey
The offset_stats parameter maintains statistics for occurrences where a series of
read or write calls from a process did not access the next sequential location. The
offset field is reset to 0 (zero) whenever a different file is read/written.
Read/write offset statistics are off, by default. The statistics can be activated by
writing anything into the offset_stats file.
Example:
# cat /proc/fs/lustre/llite/lustre-f57dee00/rw_offset_stats
snapshot_time: 1155748884.591028 (secs.usecs)
R/W PID RANGE STARTRANGE ENDSMALLEST EXTENTLARGEST EXTENTOFFSET
R 8385 0 128 128 128 0
R 8385 0 224 224 224 -128
W 8385 0 250 50 100 0
W 8385 100 1110 10 500 -150
W 8384 0 5233 5233 5233 0
R 8385 500 600 100 100 -610
Where:
Field
R/W
PID
Range Start/Range End
Description
Whether the non-sequential call was a read or write
Process ID which made the read/write call.
Range in which the read/write calls were sequential.
Smallest Extent
Largest Extent
Offset
Smallest extent (single read/write) in the corresponding range.
Largest extent (single read/write) in the corresponding range.
Difference from the previous range end to the current range start.
For example, Smallest-Extent indicates that the writes in the
range 100 to 1110 were sequential, with a minimum write of 10
and a maximum write of 500. This range was started with an
offset of -150. That means this is the difference between the last
entry’s range-end and this entry’s range-start for the same file.
The rw_offset_stats file can be cleared by writing to it:
echo > /proc/fs/lustre/llite/lustref57dee00/rw_offset_stats
Chapter 20 LustreProc 20-15