Get the Cache Hit Rate from the CLI?

michael_rodrigu — Wed, 25 May 2016 20:53:25 GMT

Is it possible to see the cache hit rate for a volume or for the whole array using a CLI command? I've looked through the reference document and saw some data related to cache using "vol --info" but couldn't find anything specifically showing the hit rate?

Re: Get the Cache Hit Rate from the CLI?

jcates98 — Wed, 01 Jun 2016 20:15:34 GMT

Hi Michael,

The vol command will show you how the volume is configured - for example what performance policy is set, whether or not caching is enabled, and what the caching policy is. It will not, however, give you any statistics as far as how many reads are actually being serviced from the cache. For that, you'll need to look to the stats command. (Or InfoSight, or the NimbleOS Web UI...)

You asked about hit rates for both a single volume and the whole array, so I'll include examples of each.

Whole Array

Nimble OS $ stats --diff --interval 5

Will use per-second statistics

Stats from 2016-06-01,12:46:45 to 2038-01-18,19:14:07

reads writes seqRead% nsMemHit% nsSsdHit% netRxKB netTxKB ssdRdKB ssdWrKB hddRdKB hddWrKB

110 214 0 100 0 18119 248 0 0 141212 740

0 230 0 0 0 11695 61 0 0 112977 792

108 206 0 100 0 18189 306 0 0 141220 2148

9 252 0 100 0 11702 202 0 0 141212 8508

2 219 0 100 0 18281 100 0 0 112970 6976

1 219 0 100 0 11992 71 0 0 141212 3468

0 179 0 0 0 18099 99 0 0 141212 1588

119 259 0 100 0 11737 77 0 0 112977 968

There are a couple of things to point out here. First, the --diff option to the stats command gives us incremental statistics rather than a running total. Next, make particular note of the nsMemHit% and nsSsdHit% fields. These represent the percentage of reads being serviced from either memory (nsMemHit%) or the flash drives (nsSsdHit%). The cache hit rate is the sum of these two fields. I have a very modest workload running on my array in this example, and all of the reads are being serviced from memory. Note that when there are no reads occurring, this percentage drops to zero.

Individual Volume

Nimble OS $ stats --diff --interval 5 --vol REPL.vmdk

Will use per-second statistics

Stats from 2016-06-01,12:47:53 to 2038-01-18,19:14:07

vol reads rdKB writes wrKB seqRead% nsMemHit% nsSsdHit% dataKB dataSnapKB

REPL.vmdk 0 0 121 8020 0 0 0 0 0

REPL.vmdk 0 0 145 15476 0 0 0 0 0

REPL.vmdk 0 0 151 13288 0 0 0 0 0

REPL.vmdk 0 0 149 15017 0 0 0 0 0

REPL.vmdk 0 0 165 13888 0 0 0 0 0

REPL.vmdk 1 2.50 161 15316 0 100 0 0 0

REPL.vmdk 6246 24984 138 10297 0 100 0 0 0

REPL.vmdk 907 3628 181 14286 0 100 0 0 0

REPL.vmdk 0 0 133 13300 0 0 0 0 0

REPL.vmdk 1 2.50 155 15058 0 100 0 0 0

REPL.vmdk 0 0 149 13809 0 0 0 0 0

REPL.vmdk 0 0 144 15038 0 0 0 0 0

REPL.vmdk 0 0 99 10050 0 0 0 0 0

This is essentially the same command line usage as the whole array option, with a volume specified on the command line using the --vol parameter. Again, the cache hit rate is the nsMemHit% plus the nsSsdHit%.

Cheers,

Julian

topic Get the Cache Hit Rate from the CLI? in Application Integration

Get the Cache Hit Rate from the CLI?

Re: Get the Cache Hit Rate from the CLI?

Whole Array

Individual Volume