Date: Thu, 23 Feb 2017 09:26:09 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: "Eric A. Borisch" <eborisch@gmail.com>, Wiktor Niesiobedzki <bsd@vink.pl> Cc: "freebsd-fs@freebsd.org" <freebsd-fs@FreeBSD.org>, "Eugene M. Zheganin" <emz@norma.perm.ru> Subject: Re: zfs raidz overhead Message-ID: <d744e518-943e-52e8-55c8-1bd772e02b1e@FreeBSD.org> In-Reply-To: <CAASnNnoLP32REdLMPcm0G6jR=wYLNH9V6uqRH=u-ukrE2G7RZA@mail.gmail.com> References: <1b54a2fe35407a95edca1f992fa08a71@norman-vivat.ru> <CAASnNnpB7NFWUbBLxKidXzsDMAwzcJzRc_f4R-9JG_=BZ9fA%2BA@mail.gmail.com> <CAH17caWPRtJVpTQNrqaabtYt7xR%2Boc-eL87tvea=pXjG12oEJg@mail.gmail.com> <CAASnNnoLP32REdLMPcm0G6jR=wYLNH9V6uqRH=u-ukrE2G7RZA@mail.gmail.com>
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On 23/02/2017 02:49, Eric A. Borisch wrote: > On Wed, Feb 22, 2017 at 3:50 PM, Wiktor Niesiobedzki <bsd@vink.pl> wrote: > >> I can add to this, that this is not only seen on raidz, but also on >> mirror pools, such as this: >> # zpool status tank >> pool: tank >> state: ONLINE >> scan: scrub repaired 0 in 3h22m with 0 errors on Thu Feb 9 06:47:07 2017 >> config: >> >> NAME STATE READ WRITE CKSUM >> tank ONLINE 0 0 0 >> mirror-0 ONLINE 0 0 0 >> gpt/tank1.eli ONLINE 0 0 0 >> gpt/tank2.eli ONLINE 0 0 0 >> >> errors: No known data errors >> >> >> When I createted test zvols: >> # zfs create -V10gb -o volblocksize=8k tank/tst-8k >> # zfs create -V10gb -o volblocksize=16k tank/tst-16k >> # zfs create -V10gb -o volblocksize=32k tank/tst-32k >> # zfs create -V10gb -o volblocksize=64k tank/tst-64k >> # zfs create -V10gb -o volblocksize=128k tank/tst-128k >> >> # zfs get used tank/tst-8k >> NAME PROPERTY VALUE SOURCE >> tank/tst-8k used 10.3G - >> root@kadlubek:~ # zfs get used tank/tst-16k >> NAME PROPERTY VALUE SOURCE >> tank/tst-16k used 10.2G - >> root@kadlubek:~ # zfs get used tank/tst-32k >> NAME PROPERTY VALUE SOURCE >> tank/tst-32k used 10.1G - >> root@kadlubek:~ # zfs get used tank/tst-64k >> NAME PROPERTY VALUE SOURCE >> tank/tst-64k used 10.0G - >> root@kadlubek:~ # zfs get used tank/tst-128k >> NAME PROPERTY VALUE SOURCE >> tank/tst-128k used 10.0G - > > > Nope, that all looks correct. There is space reserved for metadata > (checksum for example) when you create a zvol. Since checksums are computed > by block, it makes sense that more metadata is required for the 8k > volblocksize. Also, the smaller the data blocks the more indirect blocks are needed to cover the same size. -- Andriy Gapon
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