SCF Reference Manual for the Storage Subsystem (G06.24+, H06.03+)

Displaying Information About Magnetic Disks
SCF Reference Manual for the Storage Subsystem—529937-007
5-16
Displaying Disk Cache Statistics
Blocks
Requested
the default number of cache blocks that are requested.
Blocks Allocated the number of cache blocks allocated.
Blocks In Use the number of cache blocks containing a valid disk block in
memory.
Blocks Dirty the percentage of allocated blocks that are currently dirty (blocks
in cache that have been changed but are not yet written back to
disk).
Cache Reads the percentage of cache calls that the disk process made for user
read requests. (When added together, the percentages displayed
for Cache Reads and Cache Writes equal 100 percent.)
Cache Read
Hits
the percentage of cache reads when the requested block was
found in cache memory. (When added together, the percentages
displayed for Cache Read Hits and Cache Read Misses equal
100 percent.)
This value should be a high percentage, indicating that the
requested blocks are frequently found in cache. If the percentage
is low and you want to raise it, increase the size of cache by
using the ALTER DISK, CACHE command. For more information,
see Configuring the Size of Disk Cache on page 6-23.
Cache Read
Misses
the percentage of cache reads when the disk process could not
find the requested block in cache and had to bring the block in
from disk. A user write request does not affect the read counters
even if the cache write request causes a disk read. If this
percentage becomes very high, consider increasing the size of
cache. For more information, see Configuring the Size of Disk
Cache on page 6-23.
Cache Writes the percentage of cache calls that the disk process made for user
write requests and that resulted in cache writes. (When added
together, the percentages displayed for Cache Reads and Cache
Writes equal 100 percent.)
Cache Write
Dirties
the percentage of cache writes for which the block was found
changed (dirty). When new data is inserted into a block and the
disk process finds a dirty block, it does not have to perform a disk
read but it must perform a disk write.
Having a large value for Cache Write Dirties reduces the number
of required physical I/O operations (that is, disk reads and disk
writes).