From owner-freebsd-fs@freebsd.org Thu Feb 23 07:27:36 2017 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id BB454CEAB4B for ; Thu, 23 Feb 2017 07:27:36 +0000 (UTC) (envelope-from avg@FreeBSD.org) Received: from citapm.icyb.net.ua (citapm.icyb.net.ua [212.40.38.140]) by mx1.freebsd.org (Postfix) with ESMTP id 1749BDB0 for ; Thu, 23 Feb 2017 07:27:35 +0000 (UTC) (envelope-from avg@FreeBSD.org) Received: from porto.starpoint.kiev.ua (porto-e.starpoint.kiev.ua [212.40.38.100]) by citapm.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id JAA29348; Thu, 23 Feb 2017 09:27:31 +0200 (EET) (envelope-from avg@FreeBSD.org) Received: from localhost ([127.0.0.1]) by porto.starpoint.kiev.ua with esmtp (Exim 4.34 (FreeBSD)) id 1cgnoI-000Ohv-VA; Thu, 23 Feb 2017 09:27:30 +0200 Subject: Re: zfs raidz overhead To: "Eric A. Borisch" , Wiktor Niesiobedzki References: <1b54a2fe35407a95edca1f992fa08a71@norman-vivat.ru> Cc: "freebsd-fs@freebsd.org" , "Eugene M. Zheganin" From: Andriy Gapon Message-ID: Date: Thu, 23 Feb 2017 09:26:09 +0200 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 23 Feb 2017 07:27:36 -0000 On 23/02/2017 02:49, Eric A. Borisch wrote: > On Wed, Feb 22, 2017 at 3:50 PM, Wiktor Niesiobedzki 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