Date: Fri, 28 Aug 2020 18:45:00 -0400 From: mike tancsa <mike@sentex.net> To: Mason Loring Bliss <mason@blisses.org>, freebsd-fs@freebsd.org Subject: Re: Maildir on ZFS Message-ID: <d706f31b-1381-8091-e7b3-e34fcb1e3d81@sentex.net> In-Reply-To: <20200828220312.GD6456@blisses.org> References: <20200828220312.GD6456@blisses.org>
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Havent done benchmarking to see what sort of difference tweaking primarycache makes on our mail server. But I tried on a very busy sftp server where some directories had 500,000+ files in them. It didnt seem to make a difference performance wise for me, at least when fiddling with min cache sizes etc. Lots of RAM and fast disks. Our mail spool is on the equiv of raid10 and thats "spinning rust" and it keeps up well. I would approach it as your hardware should be able to meet its functional requirements in the default configuration. Then, looking at zfs-stats and cache statistics, see what makes a difference for tuning. I dont think its gonna be a game changer either way. Not sure about record sizes. L2ARC doesnt seem to help for our situation (RELENG_11) ARC Efficiency: 35.40b Cache Hit Ratio: 98.39% 34.83b Cache Miss Ratio: 1.61% 571.23m Actual Hit Ratio: 98.28% 34.79b Data Demand Efficiency: 98.90% 3.45b Data Prefetch Efficiency: 75.07% 23.39m CACHE HITS BY CACHE LIST: Most Recently Used: 4.94% 1.72b Most Frequently Used: 94.94% 33.07b Most Recently Used Ghost: 0.05% 17.29m Most Frequently Used Ghost: 0.16% 54.30m CACHE HITS BY DATA TYPE: Demand Data: 9.79% 3.41b Prefetch Data: 0.05% 17.56m Demand Metadata: 87.97% 30.64b Prefetch Metadata: 2.19% 762.76m CACHE MISSES BY DATA TYPE: Demand Data: 6.62% 37.83m Prefetch Data: 1.02% 5.83m Demand Metadata: 74.66% 426.48m Prefetch Metadata: 17.70% 101.09m ------------------------------------------------------------------------ L2 ARC Summary: (HEALTHY) Passed Headroom: 29.46m Tried Lock Failures: 3.05m IO In Progress: 27.85k Low Memory Aborts: 4 Free on Write: 2.41m Writes While Full: 31.85k R/W Clashes: 0 Bad Checksums: 0 IO Errors: 0 SPA Mismatch: 17.47b L2 ARC Size: (Adaptive) 136.03 GiB Header Size: 0.11% 156.63 MiB L2 ARC Evicts: Lock Retries: 440 Upon Reading: 7 L2 ARC Breakdown: 571.23m Hit Ratio: 4.53% 25.88m Miss Ratio: 95.47% 545.35m Feeds: 10.88m L2 ARC Buffer: Bytes Scanned: 1022.25 TiB Buffer Iterations: 10.88m List Iterations: 43.51m NULL List Iterations: 362.24k L2 ARC Writes: Writes Sent: 100.00% 3.94m ---Mike On 8/28/2020 6:03 PM, Mason Loring Bliss wrote: > I sent this to BSD Now a month ago and haven't heard anything back, but I > bet there are opinions to be had in here! Thanks in advance. > > > > I'm migrating a mail server to a FreeBSD jail, and I've seen conflicting > notes about how best to tune ZFS for holding accounts with Maildirs. My > current thinking is that I don't want to change recordsize as it's an upper > limit, not a minimum, but that I might want to set primarycache=metadata so > I'm caching information about Maildir contents, but not the Maildir > contents themselves. But are these valid thoughts, and what else is there > to think about? The problem is that I don't know what I don't know, and I'm > not sure about what I do know, so I'd love some advise about how best to > tune a dataset for Maildirs. > > Thanks! >
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