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Performance Terms

This topic shows the terms and definitions that are specific to the statistics and performance of the cache task.

Total Read: Total size in bytes of read operations issued to the volume. It counts the reads done on the underlying disk and the cache.

Cached Read: Total size in bytes of read operations done on the L1 and the L2 cache. This is a subset of Total Read statistic. The number in parenthesis represents the cache hit rate.

L2Storage Read: Total size in bytes of reads from the level-2 storage. The number in parenthesis represents the level-2 cache hit rate which is calculated from the formula: L2Storage Read / Total Read * 100%.

L2Storage Write: Total size in bytes of writes to the level-2 storage.

Total Write (Req): Total size in bytes of write requests that Windows issued to the volume.

Total Write (Done): Total bytes written to the underlying disk. The number in parenthesis is calculated from the formula: Total Write (Done) / Total Write (Req) * 100%.

Urgent Write: Total size in bytes of data written to the disk from the cache by reason of insufficient free cache space. When cache space is almost full, PrimoCache has to urgently write certain amount of deferred data stored in the cache to the disk, thus provides enough cache space for new incoming data.

Normal Write: Total size in bytes of data written to the disk from the cache by reason of timer flush or manual flush operations.

Deferred Blocks: Number of cache blocks which currently stores write-data to be written to the disk. The number in parenthesis is the percentage of deferred blocks out of total cache blocks.

Trimmed Blocks: Total number of cache blocks which stored write-data but were released by TRIM command. Write-data in these cache blocks won't be written to the disk because such data is no use.

Prefetch: Indicates the prefetch state. The numbers in parenthesis refers to the total bytes prefetched (the number before backslash) and the total bytes requested to be prefetched (the number after backslash).

Free Cache (L1/L2): Size in bytes of currently free cache space for new data. The number before backslash refers to the level-1 free cache, and the number after backslash refers to the level-2 free cache. When Free Cache drops to a certain value (32MB), PrimoCache will discard or move around some cache blocks according to the cache algorithm.

Cache Hit Rate: Percentage of read-data that is found in the cache without having to read from the disk. It is calculated from the formula: Cache Hit Rate = Cached Read / Total Read * 100%.