250 DS8800 Performance Monitoring and Tuning
same data due to the nature of sequential access. In this case, defragmentation of the
filesystem improves the performance. You cannot determine whether increasing the size of
cache improves the I/O performance without knowing the characteristics of the data on your
DS8000.
We suggest that you monitor the read hit ratio over an extended period of time:
If the cache hit ratio is historically low, it is most likely due to the nature of the data access
patterns. Defragmenting the filesystem and making indexes if none exist might help more
than adding cache.
If you have a high cache hit ratio initially and it decreases as the workload increases,
adding cache or moving part of the data to volumes associated ...