Date: Tue, 15 Apr 2014 15:28:28 +0300 From: Anton Sayetsky <vsjcfm@gmail.com> To: freebsd-fs <freebsd-fs@freebsd.org> Subject: ZFS prefetch efficiency Message-ID: <CAFG2KCK_AxGAug%2BCWUCCsPPqeSGw%2Bp5XxxxsVTjBE7wOkqm6=w@mail.gmail.com>
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Hello, I have a machine with 256 G RAM almost all dedicated to ARC. zfs-stats shows the following: root@cs0:~# zfs-stats -EZ ------------------------------------------------------------------------ ZFS Subsystem Report Tue Apr 15 15:25:10 2014 ------------------------------------------------------------------------ ARC Efficiency: 1.07b Cache Hit Ratio: 73.53% 788.04m Cache Miss Ratio: 26.47% 283.62m Actual Hit Ratio: 64.30% 689.08m Data Demand Efficiency: 99.69% 359.48m Data Prefetch Efficiency: 31.54% 409.48m CACHE HITS BY CACHE LIST: Anonymously Used: 10.38% 81.78m Most Recently Used: 38.09% 300.13m Most Frequently Used: 49.36% 388.95m Most Recently Used Ghost: 0.56% 4.45m Most Frequently Used Ghost: 1.62% 12.74m CACHE HITS BY DATA TYPE: Demand Data: 45.48% 358.38m Prefetch Data: 16.39% 129.15m Demand Metadata: 37.79% 297.81m Prefetch Metadata: 0.34% 2.69m CACHE MISSES BY DATA TYPE: Demand Data: 0.39% 1.10m Prefetch Data: 98.84% 280.33m Demand Metadata: 0.76% 2.16m Prefetch Metadata: 0.01% 39.25k ------------------------------------------------------------------------ File-Level Prefetch: (HEALTHY) DMU Efficiency: 3.30b Hit Ratio: 91.98% 3.04b Miss Ratio: 8.02% 264.94m Colinear: 264.94m Hit Ratio: 0.01% 20.57k Miss Ratio: 99.99% 264.92m Stride: 2.77b Hit Ratio: 99.99% 2.77b Miss Ratio: 0.01% 245.81k DMU Misc: Reclaim: 264.92m Successes: 0.60% 1.60m Failures: 99.40% 263.32m Streams: 270.09m +Resets: 0.06% 164.49k -Resets: 99.94% 269.93m Bogus: 0 ------------------------------------------------------------------------ root@cs0:~# I'm confused with the next 2 values: 1. Data Prefetch Efficiency: 31.54% 409.48m 2. DMU Efficiency: 3.30b Hit Ratio: 91.98% 3.04b So here is my question: is prefetch really efficient or not?
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