Viewing buffer cache activity

Buffer cache activity can be seen using sar -b (or mpsar -b for SMP):

   23:59:44 bread/s lread/s %rcache bwrit/s lwrit/s %wcache pread/s pwrit/s
   23:59:49      38     723      95       4      16      75       0       0
   23:59:54      38    1280      97       4      22      81       0       0
   23:59:59      37    1100      97       2      25      91       0       0
    
   Average       37    1006      96       3      20      83       0       0

The buffer cache write hit rate, %wcache, indicates the percentage by volume of data written to disk (or any block device) where the block in which the data was to be written was already in the buffer cache.

bread/s indicates the average number of kilobytes per second read from the block devices (including disk drives) into the the buffer cache.

bwrit/s indicates the average number of kilobytes per second written from the buffer cache to block devices by the buffer flushing daemon, bdflush.