Dell PowerVault MD3420 - Manual (Page 351)

The reason this number is lower than 100% is that each allocation unit of the SSD
cache, the SSD cache cache-block, is divided into smaller units called sub-blocks,
which are filled somewhat independently. A higher number is generally better, but
performance gains can be significant even with a smaller number.
These additional statistics are included when you save the data to a file:
Read Blocks Number of blocks in host reads.
Write Blocks Number of blocks in host writes.
Full Hit Blocks Number of block cache hits.
The full hit blocks indicate the number of blocks that have been read entirely from
SSD cache. The SSD cache is only beneficial to performance for those operations
that are full cache hits.
Partial Hits Number of host reads where at least one block, but not all blocks, were in the SSD
cache. This is an SSD cache miss where the reads were satisfied from the base
virtual disk.
Partial cache hits and partial cache hit blocks result from an operation that has only
a portion of its data in the SSD cache. In this case, the operation must get the data
from the cached HDD virtual disk. The SSD cache offers no performance benefit
for this type of hit. If the partial cache hit blocks count is higher than the full cache
hit blocks, it is possible that a different I/O characteristic type (file system, database,
or web server) could improve the performance.
Partial Hits -
Blocks Number of blocks in Partial Hits.
Partial cache hits and partial cache hit blocks result from an operation that has only
a portion of its data in the SSD cache. In this case, the operation must get the data
from the cached HDD virtual disk. The SSD cache offers no performance benefit
for this type of hit. If the partial cache hit blocks count is higher than the full cache
hit blocks, it is possible that a different I/O characteristic type (file system, database,
or web server) could improve the performance.
Misses Number of host reads where none of the blocks were in the SSD cache. This is an
SSD cache miss where the reads were satisfied from the base virtual disk.
Misses - Blocks Number of blocks in Misses.
Populate
Actions (Host
Reads) Number of host reads where data was copied from the base virtual.
Populate
Actions (Host
Reads) - Blocks Number of blocks in Populate Actions (Host Reads).
Populate
Actions (Host
Writes) Number of host writes where data was copied from the base virtual disk to the SSD
cache.
The Populate Actions (Host Writes) count may be zero for the cache configuration
settings that do not fill the cache as a result of a Write I/O operation.
351