[PATCH] Simple ARC stats in top
Andriy Gapon
avg at FreeBSD.org
Tue Jun 26 16:09:08 UTC 2012
on 26/06/2012 18:57 Mark Felder said the following:
> On Tue, 26 Jun 2012 10:55:12 -0500, Andriy Gapon <avg at freebsd.org> wrote:
>
>> Does your system also has L2 ARC?
>> If so, could you please show a value of kstat.zfs.misc.arcstats.l2_hdr_size?
>> Otherwise, it's hard for me to explain the huge difference between Max Size and
>> ARC Size.
>
> Yes, it does.
>
> zfs2# sysctl kstat.zfs.misc.arcstats.l2_hdr_size
> kstat.zfs.misc.arcstats.l2_hdr_size: 6775072568
Aha, so no mystery, those 6G in ARC are actually used by L2ARC headers.
I missed the L2 headers because I haven't used L2 yet.
I've updated arc-sizes.sh script now to account for these headers.
So the correct ARC size breakdown is: hdr_size + data_size + other_size +
l2_hdr_size, where data_size can further be broken down to mfu_size + mru_size +
anon_size.
I think that users of zfs-stats / arc_summary.pl could benefit from this knowledge
too.
(I will repeat just in case that zfs-stats mistreats kstat.zfs.misc.arcstats.p as
current MRU size whereas it is actually target MRU size)
> zfs2# zfs-stats -L
>
> ------------------------------------------------------------------------
> ZFS Subsystem Report Tue Jun 26 10:56:54 2012
> ------------------------------------------------------------------------
>
> L2 ARC Summary: (HEALTHY)
> Passed Headroom: 61
> Tried Lock Failures: 252.97k
> IO In Progress: 0
> Low Memory Aborts: 0
> Free on Write: 382.20k
> Writes While Full: 11.08k
> R/W Clashes: 270
> Bad Checksums: 0
> IO Errors: 0
> SPA Mismatch: 0
>
> L2 ARC Size: (Adaptive) 225.09 GiB
> Header Size: 2.80% 6.31 GiB
>
> L2 ARC Breakdown: 25.52m
> Hit Ratio: 87.46% 22.32m
> Miss Ratio: 12.54% 3.20m
> Feeds: 3.99m
>
> L2 ARC Buffer:
> Bytes Scanned: 42.67 TiB
> Buffer Iterations: 3.99m
> List Iterations: 255.38m
> NULL List Iterations: 219.99m
>
> L2 ARC Writes:
> Writes Sent: 100.00% 913.05k
>
> ------------------------------------------------------------------------
--
Andriy Gapon
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