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10.2.5.
Populating the Cache
The actions that read data from the HDD and then write to the SSD are called populating the
cache. Typically, this is a background operation that immediately follows a host read or
write operation. As the goal of the cache is to store frequently accessed data, not every I/O
operation should trigger a cache population, but only ones that pass a certain threshold,
implemented as a counter. There are both a populate-on-read threshold, and a populate-on-
write threshold.
Populate-on-read Threshold
When the same data block to be read over the threshold, it is called hot data and populated
to the SSD cache. The threshold must be greater than or equal to 1 in SSD read cache or
SSD read-write cache. The value is forbidden to set 0 because of no action in read cache.
The maximum of the threshold is 4. If larger than 4, the frequently accessed data is hard
into SSD cache, so there is no obvious effect.
Populate-on-write Threshold
When the same data block to be written over the threshold, it is called hot data and
populated to the SSD cache. The threshold must be greater than or equal to 0. If it is set to 0,
no action is performed for a write cache. The value must greater than or equal to 1 in SSD
read-write cache. The value is forbidden to set 0 because of no action in write cache. The
same as above, the maximum of the threshold is 4. If larger than 4, there is no obvious
effect.
Operation Process
Each cache block on a HDD volume has a read and write counter associated. When a host
requests to read data located in that cache block, the read count is increased. If the data is
not found in the cache and the read count is greater than or equal to the populate-on-read
threshold, then a cache-populate operation is performed concurrently with the host read
operation. If a cache hit occurs, the data is immediately returned from the SSD cache and a
populate operation is not performed. If the read count is smaller than the threshold, a
populate operation is not performed.
Write cases are the same scenario as read.
Summary of Contents for XCubeSAN XS5224D
Page 71: ...SANOS User Interface 49 nnnnn RPM Power Supply Local PSU n status Reset to Default Yes No...
Page 99: ...System Settings 77 Figure 6 14 System Information...
Page 315: ...Monitoring 293 Figure 13 5 Hardware Monitoring...
Page 327: ...Support and Other Resources 305 Figure 15 1 Download Service Package in the SANOS UI...
Page 331: ...Support and Other Resources 309...
