Date: Tue, 28 Aug 2012 20:50:03 +0200 From: Niki Hammler <mailinglists@nobaq.net> To: Freddie Cash <fjwcash@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: zvol + raidz issue? Message-ID: <503D12DB.3040909@nobaq.net> In-Reply-To: <CAOjFWZ6a6h_o1sq6KGN-N5Jnq9NSj6KvjEyfvEXXYrznw%2Bj8fA@mail.gmail.com> References: <503A6F9F.7070801@nobaq.net> <CAOjFWZ4Ep5ZONO%2B7UNqt36stFN_OXoMhK=83UwPpv51P8OTjfg@mail.gmail.com> <503C8AEE.1090703@nobaq.net> <CAOjFWZ6a6h_o1sq6KGN-N5Jnq9NSj6KvjEyfvEXXYrznw%2Bj8fA@mail.gmail.com>
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Am 28.08.2012 17:27, schrieb Freddie Cash: > On Tue, Aug 28, 2012 at 2:10 AM, Niki Hammler <mailinglists@nobaq.net> wrote: >> Am 26.08.2012 22:13, schrieb Freddie Cash: >>> (Sorry for top-post, sending from phone.) >>> >>> Please show the command-line used to create the zvol. Especially the >>> recordsize option. When using zvols, you have to make sure to match the >>> recordsize of the zvol to that of the filesystem used above it. >>> Otherwise, performance will be atrocious. >> >> Sorry for my third posting on this. >> Now I strictly followed your suggestion and used >> >> zfs create -b 128k -V 500g plvl5i0/zvtest >> >> (with 128k being the recordsize of the dataset in the zpool). >> >> Suddenly the write performance increased from the 2.5 MB/s to 250 MB/s >> (or 78MB/s when using bs=4096 with dd) >> >> 1.) How can this explained? >> 2.) Is there any problem when choosing -b 128k (can I always blindly >> choose -b 128k)? >> >> Remember again that the problem ONLY occurs with raidz1+zvol+force 4096 >> block alignment and in no other case! > > Most likely it has to do with the raidz stripe size and the constant > block size of the zvol causing alignment or similar issues. Yes, but I thought a zvol is merely a file in a zpool? How can it be explained that writing to a file (with the same parameters!) is OK while writing to a zvol drastically slower? Is there anything I can check/debug? I already filed a bug in FreeNAS but since this seems to be FreeBSD-related I will also file a bug report for FreeBSD. > I've also seen indications in the zfs-discuss mailing list about > optimal and sub-optimal disk configurations for the various raidz > types (wrong number of disks in the vdev leads to horrible > performance). Yes, I know this. In my case it's 3x2TB which is fine. Regards, Niki
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