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

Configuring Magnetic Disks
SCF Reference Manual for the Storage Subsystem—529937-007
6-24
Configuring the Size of Disk Cache
block size. These minimums are determined by the disk process during
initialization (that is, after a system-load or when a volume is brought up). The
minimum values are based upon a number of factors, such as the physical
memory page size and the number of disk processes. If the specified number of
blocks is below the minimum, the disk process uses the calculated minimum
number.
•
To avoid wasting unused space within a physical memory page, all allocations
round up to the next whole physical page boundary. For example, assuming a 16K
physical page size, if you specify 100 for the 512-byte cache, the actual value is
rounded up to 128 (8 physical pages). While the pages underlying the cache are
not swappable, they are available to the memory manager when not in use.
•
The maximum tested cache allocation is 900 MB. If you allocate more cache than
can be supported by the available physical and processor memory, the disk
process overrides the requested values by setting the cache sizes to default values
(.5K,18), (1K,18), (2K,18), (4K,1024).
•
On occasion, the memory needs of the rest of the system might prevent the disk
process from actually using the allocated cache.
Configuring Disk Cache
1. Review information about the CACHE attribute on page 14-56.
2. List current disk cache configuration information:
-> INFO $DATA10, CACHE
STORAGE - Cache Information Magnetic DISK \COMM.$DATA10
Cache Block Size ________________512_________1024_________2048_________4096_
*Blocks Requested: -1 -1 -1 -1
Blocks Allocated: 160 144 144 1024
Bytes Allocated To Cache: 4608 K