sar -b

[Ashwin_4]

Hi Masters,
I'm pasting the output of sar -b 4 5 below, is it indicates write cache problem in the system if yes what action i should take.

16:56:53 bread/s lread/s %rcache bwrit/s lwrit/s %wcache pread/s pwrit/s
16:56:57 0 467 100 5 6 17 0 0
16:57:01 0 342 100 4 4 6 0 0
16:57:05 0 334 100 2 3 36 0 0
16:57:09 0 334 100 3 2 0 0 0
16:57:13 0 336 100 3 3 0 0 0

Average 0 363 100 3 4 9 0 0

Thanks

[Joseph Loo]

hi,

observe a little longer, maybe "sar -b 5 30" before making sure if the buffer cache is the bottleneck.

take note that %rcache >=90% and %wcache >=70% is a desirable figure.

regards.

[Shaikh Imran]

Hi,
I don't think its write cache problem.
How are you comnig to this conclusion ?
sar -b
This command reports buffer activity.
bread/s : Number of physical reads per second from the disk (or other block devices)
to the buffer cache
bwrit/s : Number of physical writes per second from the buffer cache to the disk (or
other block device)
lread/s : Number of reads per second from buffer cache
lwrit/s : Number of writes per second to buffer cache
%rcache : Buffer cache hit ratio for read requests e.g., 1 - bread/lread
%wcache : Buffer cache hit ratio for write requests e.g., 1 - bwrit/lwrit
pread/s : Number of reads per second from character device using the physio()
(raw I/O) mechanism
pwrit/s : Number of writes per second to character device using the physio()
(i.e., raw I/O) mechanism mechanism.

What are you trying to monitor ?

you can try sar -d sar -u etc.., also

Regards,

[Bruno Ganino]

I don't see nothing problem here.
Bruno

[RAC_1]

you need to observe it for littelt longer. sar -b 2 50.

If write cache rate is not constantly aroung 80 %, you can very well reduce buffer cache and make that saved memory available to users. What you run on this box?

My experience shows that with buffer cache set 300-800 mb, gives good performance. The buffer read and write chache hits are good enough around 85-90 %, so that buffer cache is effectively used.

Anil