If you feel the need to micro manage the arc here are the parameters
you'll like:
zfs_arc_max
zfs_arc_min
you need/should to specify values in 64 bits. ie.
* limit size of arc for hadoop systems
set zfs:zfs_arc_max = 0x900000000
or conversely
set zfs:zfs_arc_min = 0x800000000
understand that by nailing down the minimize size you are setting
yourself up for memory starvation problems if you dont also tightly
control memory usage. I dont use zfs_arc_min for this reason.
here is the oracle page on the tuneable, for that is worth.
http://docs.oracle.com/cd/E19253-01/817-0404/gjheb/index.html
j.
On 3/12/15 7:37 AM, Sebastian Gabler wrote:
Hi,
I have 12 GB RAM, 20 GB total pool size machine. L2ARC for one pool is
107G SSD. I am wondering a bit about:
- why not more of the RAM is used by ARC (I have run the ARC
optimisation script from the evil tuning guide, there machine is file
server exclusively, so no other apps steal RAM)
- why the hit rate on the l2ARC is rather small (is it because the hit
rate on ARC is rather ok, which is what I think?)
- would it help the quality of the service I am providing trying to
increase the prefetch hit rate, and how could I achieve that if.
Sample from arcstat:
time hit% dh% ph% mh% l2hit% arcsz
14:20:52 92 99 27 99 1 4.5G 4.5G
14:21:52 92 99 28 99 1 4.5G 4.5G
14:22:52 92 99 31 99 1 4.7G 4.7G
14:23:52 93 99 30 99 1 4.5G 4.5G
14:24:52 92 99 27 99 1 4.5G 4.5G
14:25:52 92 99 30 99 1 4.5G 4.5G
14:26:53 92 99 27 97 1 4.5G 4.5G
14:27:53 93 99 30 99 1 4.5G 4.5G
14:28:53 92 99 28 99 1 4.5G 4.5G
14:29:53 93 99 29 99 1 4.5G 4.5G
14:30:53 92 99 28 99 1 4.5G 4.5G
14:31:53 92 99 30 99 1 4.5G 4.5G
14:32:53 93 98 30 99 2 4.5G 4.5G
14:33:53 92 99 28 99 1 4.5G 4.5G
14:34:53 92 99 27 99 1 4.5G 4.5G
14:35:53 92 99 32 99 1 4.6G 4.6G
14:36:53 89 98 32 99 0 4.5G 4.5G
14:37:53 92 99 30 99 1 4.5G 4.5G
14:38:53 92 99 28 99 1 4.5G 4.5G
14:39:53 93 99 28 98 2 4.5G 4.5G
14:40:53 93 99 29 99 1 4.5G 4.5G
Thanks for any hints,
Sebastian
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