Display buffer activity statistics with the sar -b command.
The buffer is used to cache metadata. Metadata includes inodes, cylinder group blocks, and indirect blocks.
$ sar -b 00:00:00 bread/s lread/s %rcache bwrit/s lwrit/s %wcache pread/s pwrit/s 01:00:00 0 0 100 0 0 55 0 0 |
The following example of sar -b command output shows that the %rcache and %wcache buffers are not causing any slowdowns. All the data is within acceptable limits.
$ sar -b SunOS balmyday 5.10 s10_51 sun4u 03/18/2004 00:00:04 bread/s lread/s %rcache bwrit/s lwrit/s %wcache pread/s pwrit/s 01:00:00 0 0 100 0 0 94 0 0 02:00:01 0 0 100 0 0 94 0 0 03:00:00 0 0 100 0 0 92 0 0 04:00:00 0 1 100 0 1 94 0 0 05:00:00 0 0 100 0 0 93 0 0 06:00:00 0 0 100 0 0 93 0 0 07:00:00 0 0 100 0 0 93 0 0 08:00:00 0 0 100 0 0 93 0 0 08:20:00 0 1 100 0 1 94 0 0 08:40:01 0 1 100 0 1 93 0 0 09:00:00 0 1 100 0 1 93 0 0 09:20:00 0 1 100 0 1 93 0 0 09:40:00 0 2 100 0 1 89 0 0 10:00:00 0 9 100 0 5 92 0 0 10:20:00 0 0 100 0 0 68 0 0 10:40:00 0 1 98 0 1 70 0 0 11:00:00 0 1 100 0 1 75 0 0 Average 0 1 100 0 1 91 0 0 |
The following table describes the buffer activities that are displayed by the -b option.
Field Name |
Description |
---|---|
bread/s |
Average number of reads per second that are submitted to the buffer cache from the disk |
lread/s |
Average number of logical reads per second from the buffer cache |
%rcache |
Fraction of logical reads that are found in the buffer cache (100 % minus the ratio of bread/s to lread/s) |
bwrit/s |
Average number of physical blocks (512 blocks) that are written from the buffer cache to disk, per second |
lwrit/s |
Average number of logical writes to the buffer cache, per second |
%wcache |
Fraction of logical writes that are found in the buffer cache (100 % minus the ratio of bwrit/s to lwrit/s) |
pread/s |
Average number of physical reads, per second, that use character device interfaces |
pwrit/s |
Average number of physical write requests, per second, that use character device interfaces |
The most important entries are the cache hit ratios %rcache and %wcache. These entries measure the effectiveness of system buffering. If %rcache falls below 90 percent, or if %wcache falls below 65 percent, it might be possible to improve performance by increasing the buffer space.