Date: Mon, 30 Nov 2015 09:17:33 +0000 From: krad <kraduk@gmail.com> To: Kai Gallasch <k@free.de> Cc: FreeBSD FS <freebsd-fs@freebsd.org> Subject: Re: High fragmentation on zpool log Message-ID: <CALfReycnyrH3rSAwUUCJGp9BVSC6TgJ=0TrYNh4P-=o8p==8Ew@mail.gmail.com> In-Reply-To: <565875A7.6060004@free.de> References: <565875A7.6060004@free.de>
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Fragmentation isn't really a big issue on SSD's as there are no heads to move around like on magnetic drives. Also due to wear levelling, you actually have no idea where a block actually is on a memory cell, as the drive only gives a logical representation of the layout of blocks, not an actual true mapping. On 27 November 2015 at 15:24, Kai Gallasch <k@free.de> wrote: > > Hi. > > Today I had a look at the zpool of a server (FreeBSD 10.2, GENERIC > kernel, 100d uptime, 96GB RAM) I recently installed. > > The pool has eight SAS drives in a raid 10 setup (concatenated mirror > pairs) and uses a cache and a mirrored log. > > The log and cache both are on a pair of Intel SSDs. > > # gpart show -l da9 > => 34 195371501 da9 GPT (93G) > 34 6 - free - (3.0K) > 40 16777216 1 log-BTTV5234003K100FGN (8.0G) > 16777256 178594272 2 cache-BTTV5234003K100FGN (85G) > 195371528 7 - free - (3.5K) > > > Is 85% fragmentation of the log device something to worry about? > > Why does zpool list show so unrealistic values for FREE and CAP? > Is this normal? > > Atached: Some output of zpool list. > > Regards, > Kai. > > > (zpool list -v output, ommited columns: EXPANDSZ.,DEDUP, > HEALTH, ALTROOT) > > NAME SIZE ALLOC FREE FRAG CAP > rpool 7.25T 440G 6.82T 4% 5% > mirror 1.81T 110G 1.71T 4% 5% > gpt/rpool-WMC160D0SVZE - - - - - > gpt/rpool-WMC160D8MJPD - - - - - > mirror 1.81T 110G 1.70T 4% 5% > gpt/rpool-WMC160D9DLL2 - - - - - > gpt/rpool-WMC160D23CWA - - - - - > mirror 1.81T 110G 1.71T 4% 5% > gpt/rpool-WMC160D94930 - - - - - > gpt/rpool-WMC160D9V5LW - - - - - > mirror 1.81T 110G 1.71T 4% 5% > gpt/rpool-WMC160D9ZV0S - - - - - > gpt/rpool-WMC160D5HFT6 - - - - - > mirror 7.94G 43.2M 7.90G 85% 0% > gpt/log-BTTV523401U4100FGN - - - - - > gpt/log-BTTV5234003K100FGN - - - - - > cache - - - - - > gpt/cache-BTTV5234003K100FGN 85.2G 142G 16.0E 0% 166% > gpt/cache-BTTV523401U4100FGN 85.2G 172G 16.0E 0% 202% > > > > -- > PGP-KeyID = 0x70654D7C4FB1F588 > > > >
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