Date: Tue, 26 Jun 2012 19:08:50 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: Mark Felder <feld@feld.me>, John Baldwin <jhb@FreeBSD.org> Cc: freebsd-fs@FreeBSD.org Subject: Re: [PATCH] Simple ARC stats in top Message-ID: <4FE9DE92.3040700@FreeBSD.org> In-Reply-To: <op.wgio9gg934t2sn@tech304> References: <201206251443.41768.jhb@freebsd.org> <op.wgik62ia34t2sn@tech304> <4FE9CC00.9090501@FreeBSD.org> <op.wgins2ez34t2sn@tech304> <4FE9DB60.1030905@FreeBSD.org> <op.wgio9gg934t2sn@tech304>
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on 26/06/2012 18:57 Mark Felder said the following: > On Tue, 26 Jun 2012 10:55:12 -0500, Andriy Gapon <avg@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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