Reducing disk activity caused by swapping and paging

To estimate the impact that paging in from filesystems has on disk activity, multiply the value of pgfil/s reported by sar -p (or mpsar -p for SMP) by 8 to convert from 4KB pages to the number of 512-byte disk blocks read or written per second:

Disk activity due to paging in = 8 pgfil/s

The amount of disk activity caused by swapping and paging out to the swap areas can be estimated from the values of bswin/s and bswot/s reported by sar -w (or mpsar -w for SMP):

Disk activity due to swapping = 8 (bswin/s + bswot/s)

These values can be compared with the total number number of blocks per second being transferred to and from the disks containing the filesystems and swap areas. Use sar -d (or mpsar -p for SMP) to report the number of blocks transferred per second (blks/s). See ``Viewing disk and other block I/O activity'' for more information about monitoring hard disk activity.

If a high proportion of disk activity is caused by paging in, and this is causing a disk bottleneck, see ``Tuning disk I/O-bound systems'' for suggested ways to cure this.

If swapping and paging out is causing a disk bottleneck, you could create swap areas on several disks to relieve the load on a single disk. However, it is far better to reduce the memory shortage.