[OpenIndiana-discuss] Arc and L2arc hit rate

[Sebastian Gabler]

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