Hello.
I got an idea.. How about creating an ramdisk, making a pool out of it,
then making compressed zvols and add those as l2arc.. Instant compressed
arc ;)
So I did some tests with secondarycache=metadata...
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
ftp 5.07T 1.78T 198 17 11.3M 1.51M
raidz2 1.72T 571G 58 5 3.78M 514K
...
raidz2 1.64T 656G 75 6 3.78M 524K
...
raidz2 1.70T 592G 64 5 3.74M 512K
...
cache - - - - - -
/dev/zvol/dsk/ramcache/ramvol 84.4M 7.62M 4 17 45.4K 233K
/dev/zvol/dsk/ramcache/ramvol2 84.3M 7.71M 4 17 41.5K 233K
/dev/zvol/dsk/ramcache/ramvol3 84M 8M 4 18 42.0K 236K
/dev/zvol/dsk/ramcache/ramvol4 84.8M 7.25M 3 17 39.1K 225K
/dev/zvol/dsk/ramcache/ramvol5 84.9M 7.08M 3 14 38.0K 193K
NAME RATIO COMPRESS
ramcache/ramvol 1.00x off
ramcache/ramvol2 4.27x lzjb
ramcache/ramvol3 6.12x gzip-1
ramcache/ramvol4 6.77x gzip
ramcache/ramvol5 6.82x gzip-9
This was after 'find /ftp' had been running for about 1h, along with all
the background noise of its regular nfs serving tasks.
I took an image of the uncompressed one (ramvol) and ran that through
regular gzip and got 12-14x compression, probably due to smaller block
size (default 8k) in the zvols.. So I tried with both 8k and 64k..
After not running that long (but at least filled), I got:
NAME RATIO COMPRESS VOLBLOCK
ramcache/ramvol 1.00x off 8K
ramcache/ramvol2 5.57x lzjb 8K
ramcache/ramvol3 7.56x lzjb 64K
ramcache/ramvol4 7.35x gzip-1 8K
ramcache/ramvol5 11.68x gzip-1 64K
Not sure how to measure the cpu usage of the various compression levels
for (de)compressing this data.. It does show that having metadata in
ram compressed could be a big win though, if you have cpu cycles to
spare..
Thoughts?
/Tomas
--
Tomas Ögren, st...@acc.umu.se, http://www.acc.umu.se/~stric/
|- Student at Computing Science, University of Umeå
`- Sysadmin at {cs,acc}.umu.se - 070-5858487
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