Dell PowerVault MD3420 - Manual (Page 350)

Parameter Description
If you do not specify a RAID controller module, the
default value is both.
file The file path and the file name to which you want
to save the SSD cache statistics. Additional
statistics are available when you save the statistics
to a file.
Enclose the file name in double quotation marks ("
"). For example: file="C:\Program Files\CLI\logs
\statistics.csv".
Notes
The following statistics are displayed on the screen:
Reads Total number of host reads of SSD cache-enabled virtual disks.
Compare the Reads relative to Writes. The Reads need to be greater than the
Writes for effective SSD cache operation. The greater the ratio of Reads to Writes
the better the operation of the cache.
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:
• 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.
Cache
Allocation (%) The amount of SSD cache storage that is allocated, expressed as a percentage of
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
Utilization (%) The amount of SSD cache storage that contains data from enabled virtual disks,
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.
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