[Bug 216364] ZFS ARC cache is duplicating data? The cache size gets bigger then the pool.

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=216364

            Bug ID: 216364
           Summary: ZFS ARC cache is duplicating data? The cache size gets
                    bigger then the pool.
           Product: Base System
           Version: 11.0-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: misc
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: k_georgiev at deltanews.bg
                CC: freebsd-amd64 at FreeBSD.org
                CC: freebsd-amd64 at FreeBSD.org

Hello,

I got system with only one pool 6G:

root at varnish:~ # zpool list
NAME    SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
zroot  5.97G  3.76G  2.21G         -    73%    62%  1.00x  ONLINE  -

However about 4-5 days after the system was powered on the ARC cache got bigger
than the pool and it stays like this:

                                                                               
    up 20+20:50:56  10:44:15
34 processes:  1 running, 33 sleeping
CPU:     % user,     % nice,     % system,     % interrupt,     % idle
Mem: 18M Active, 601M Inact, 13G Wired, 1801M Free
ARC: 12G Total, 1920M MFU, 10G MRU, 419K Anon, 40M Header, 377M Other
Swap: 2048M Total, 2048M Free


And note that the pool is 6G, but it's not even 100% full.

Even only the MFU is larger than the entire pool. There's no way that data is
not duplicated there. 

Here is output of zfs stats:


root at varnish:~ # zfs-stats -A

------------------------------------------------------------------------
ZFS Subsystem Report                            Sun Jan 22 10:45:47 2017
------------------------------------------------------------------------

ARC Summary: (HEALTHY)
        Memory Throttle Count:                  0

ARC Misc:
        Deleted:                                65.44k
        Recycle Misses:                         0
        Mutex Misses:                           4
        Evict Skips:                            1

ARC Size:                               84.86%  12.33   GiB
        Target Size: (Adaptive)         85.07%  12.36   GiB
        Min Size (Hard Limit):          12.50%  1.82    GiB
        Max Size (High Water):          8:1     14.53   GiB

ARC Size Breakdown:
        Recently Used Cache Size:       81.34%  10.06   GiB
        Frequently Used Cache Size:     18.66%  2.31    GiB

ARC Hash Breakdown:
        Elements Max:                           171.10k
        Elements Current:               87.74%  150.12k
        Collisions:                             1.69m
        Chain Max:                              4
        Chains:                                 5.03k

------------------------------------------------------------------------

-- 
You are receiving this mail because:
You are on the CC list for the bug.