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Writes
Total number of host writes to SSD cache-enabled virtual disks.
Cache Hits
A count of the number of cache hits.
Cache Hits (%)
Derived from Cache Hits/total reads.
The Cache Hit percentage should be greater than 50% for effective SSD cache
operation. A small number could be indicative of several things:
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Cache
The amount of SSD cache storage that is allocated, expressed as a percentage of
Allocation (%)
the SSD cache storage that is available to this RAID controller module. Derived
from allocated bytes / available bytes.
Cache Allocation percentage normally shows as 100%. If this number is less than
100%, it means either the cache has not been warmed or the SSD cache capacity is
larger than all the data being accessed. In the latter case, a smaller SSD cache
capacity could provide the same level of performance. Note that this does not
indicate that cached data has been placed into the SSD cache, it is simply a
preparation step before data can be placed in the SSD cache.
Cache
The amount of SSD cache storage that contains data from enabled virtual disks,
Utilization (%)
expressed as a percentage of SSD cache storage that is allocated. This value
represents the utilization or density of the SSD cache. Derived from user data
bytes / allocated bytes.
Cache Utilization percentage normally is lower than 100%, perhaps much lower.
This number shows the percent of SSD cache capacity that is filled with cache data.
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
340
Ratio of Reads to Writes is too small
Reads are not repeated
Cache capacity is too small
NOTE: To help determine the ideal SSD cache capacity, you can run the
Performance Modeling Tool using the start ssdCache [ssdCacheName]
performanceModeling command.
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