
is not feasible in
For prefetching, the cache management uses tracks. To detect a sequential access pattern, counters are maintained with every track, to record if a track has been accessed together with its predecessor. Sequential prefetching becomes active only when these counters suggest a sequential access pattern. In this manner, the DS6000/DS8000 monitors application
Just the page requested.
That page requested plus remaining data on the disk track.
An entire disk track (or a set of disk tracks) which has (have) not yet been requested.
The decision of when and what to prefetch is essentially made on a
To decide which pages are evicted when the cache is full, sequential and random
RANDOMSEQ
MRU
LRU
MRU
LRU
RANDOM bottom
Desired size
SEQ bottom
Figure 2-5 Cache lists of the SARC algorithm for random and sequential data
To follow workload changes, the algorithm trades cache space between the RANDOM and SEQ lists dynamically and adaptively. This makes SARC
28DS6000 Series: Concepts and Architecture