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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 -
Number of blocks in Partial Hits.
Blocks
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
Number of host reads where data was copied from the base virtual.
Actions (Host
Reads)
Populate
Number of blocks in Populate Actions (Host Reads).
Actions (Host
Reads) - Blocks
Populate
Number of host writes where data was copied from the base virtual disk to the SSD
Actions (Host
cache.
Writes)
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.
Populate
Number of blocks in Populate Actions (Host Writes).
Actions (Host
Writes) - Blocks
Invalidate
Number of times data was invalidated/removed from the SSD cache. A cache
Actions
invalidate operation is performed for every host write request, every host read
request with Forced Unit Access (FUA), every verify request, and in some other
circumstances.
Recycle
Number of times that the SSD cache block has been reused for another base virtual
Actions
disk and/or a different LBA range.
For effective cache operation, it is important that the number of recycles is small
compared to the combined number of read and write operations. If the number of
Recycle Actions is close to the combined number of Reads and Writes, then the
SSD cache is thrashing. Either the cache capacity needs to be increased or the
workload is not favorable for use with SSD cache.
Available Bytes
Number of bytes available in the SSD cache for use by this RAID controller module.
The available bytes, allocated bytes, and user data bytes are used to compute the
Cache Allocation % and the Cache Utilization %.
Allocated Bytes
Number of bytes allocated from the SSD cache by this RAID controller module.
Bytes allocated from the SSD cache may be empty or they may contain data from
base virtual disks.
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