[OpenIndiana-discuss] Is there anything I can do to tune caching

[Grant Albitz]

I just completed my server and I am generally happy with it. I am running openindiana on a dell r510 with 64gb of memory and 12 2tb 7200rpm sas drives. I have 2 256g Samsung 830s as l2arche. I have noticed a few things. First the l2arche is basically not being populated at all (only 20g or so). Also when running a crystaldisk benchmark against the lun on the zfs server, small writes seem to goto ram. If I perform a test with 100m I get about 800MB/s writes. If I increase that to 500m I get only about 80MB/s. It seems that the larger writes go directly to the disk. I have disabled zil with the expectation that all writes would goto ram but this may not be the case. Below are some numbers that I pulled. Is there anyway to increase l2arche usage and also ram usage? I understand that the l2arch may not be populated if most of the activity can fit in the ram (and it probably can, my total used space is only 300gigs and right now I am testing this with single user access). But if the reason l2arch isn't being populated is due to ram availability, then why are some of my writes skipping ram and going directly to the disk?

ARC syncronous write cache
System Memory:
        Physical RAM: 65515 MB
        Free Memory : 10187 MB
        LotsFree:     1023 MB

ZFS Tunables (/etc/system):

ARC Size:
        Current Size:             48921 MB (arcsize)
        Target Size (Adaptive):   48921 MB (c)
        Min Size (Hard Limit):    8061 MB (zfs_arc_min)
        Max Size (Hard Limit):    64491 MB (zfs_arc_max)

ARC Size Breakdown:
        Most Recently Used Cache Size:        93%    45557 MB (p)
        Most Frequently Used Cache Size:       6%    3364 MB (c-p)

ARC Efficency:
        Cache Access Total:            72661651
        Cache Hit Ratio:      84%     61140347      [Defined State for buffer]
        Cache Miss Ratio:     15%     11521304      [Undefined State for Buffer]
        REAL Hit Ratio:       76%     55338630      [MRU/MFU Hits Only]

        Data Demand   Efficiency:    97%
        Data Prefetch Efficiency:    35%

        CACHE HITS BY CACHE LIST:
          Anon:                        8%      5398251               [ New Customer, First Cache Hit ]
          Most Recently Used:         44%      27083442 (mru)        [ Return Customer ]
          Most Frequently Used:       46%      28255188 (mfu)        [ Frequent Customer ]
          Most Recently Used Ghost:    0%      141042 (mru_ghost)    [ Return Customer Evicted, Now Back ]
          Most Frequently Used Ghost:  0%      262424 (mfu_ghost)    [ Frequent Customer Evicted, Now Back ]
        CACHE HITS BY DATA TYPE:
          Demand Data:                65%      40237050
          Prefetch Data:               9%      5777420
          Demand Metadata:            24%      15098015
          Prefetch Metadata:           0%      27862
        CACHE MISSES BY DATA TYPE:
          Demand Data:                 7%      864227
          Prefetch Data:              91%      10540593
          Demand Metadata:             0%      112421
          Prefetch Metadata:           0%      4063
---------------------------------------------


pool

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PSC.Net

442G

10.4T

0

0

0

0

mirror

73.6G

1.74T

0

0

0

0

c2t0d0

-

-

0

0

0

0

c2t1d0

-

-

0

0

0

0

mirror

73.8G

1.74T

0

0

0

0

c2t2d0

-

-

0

0

0

0

c2t3d0

-

-

0

0

0

0

mirror

73.8G

1.74T

0

0

0

0

c2t4d0

-

-

0

0

0

0

c2t5d0

-

-

0

0

0

0

mirror

73.8G

1.74T

0

0

0

0

c2t6d0

-

-

0

0

0

0

c2t7d0

-

-

0

0

0

0

mirror

73.7G

1.74T

0

0

0

0

c2t8d0

-

-

0

0

0

0

c2t9d0

-

-

0

0

0

0

mirror

73.8G

1.74T

0

0

0

0

c2t10d0

-

-

0

0

0

0

c2t11d0

-

-

0

0

0

0

cache

-

-

-

-

-

-

c2t12d0p2

24.8G

194G

0

0

0

0

c2t13d0p2

24.4G

194G

0

0

0

0