Date: Wed, 23 Jan 2013 13:23:47 -0800 From: Artem Belevich <art@freebsd.org> To: Mark Felder <feld@feld.me> Cc: freebsd-fs <freebsd-fs@freebsd.org>, Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>, Chris Rees <utisoft@gmail.com>, FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: ZFS regimen: scrub, scrub, scrub and scrub again. Message-ID: <CAFqOu6gcvTEYCtLEUoyd4tX7acrk=V85u4EuNiDWVj4X%2B0Dcpg@mail.gmail.com> In-Reply-To: <op.wrdudwx334t2sn@markf.office.supranet.net> References: <CACpH0Mf6sNb8JOsTzC%2BWSfQRB62%2BZn7VtzEnihEKmEV2aO2p%2Bw@mail.gmail.com> <alpine.BSF.2.00.1301211201570.9447@wojtek.tensor.gdynia.pl> <20130122073641.GH30633@server.rulingia.com> <alpine.BSF.2.00.1301232121430.1659@wojtek.tensor.gdynia.pl> <CADLo838Rst7wEtV7DpY23XjpcFCsOkrN=axE1AscyO7vYgSKSg@mail.gmail.com> <op.wrdudwx334t2sn@markf.office.supranet.net>
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On Wed, Jan 23, 2013 at 1:09 PM, Mark Felder <feld@feld.me> wrote: > On Wed, 23 Jan 2013 14:26:43 -0600, Chris Rees <utisoft@gmail.com> wrote: > >> >> So we have to take your word for it? >> Provide a link if you're going to make assertions, or they're no more than >> your own opinion. > > > I've heard this same thing -- every vdev == 1 drive in performance. I've > never seen any proof/papers on it though. "1 drive in performance" only applies to number of random i/o operations vdev can perform. You still get increased throughput. I.e. 5-drive RAIDZ will have 4x bandwidth of individual disks in vdev, but would deliver only as many IOPS as the slowest drive as record would have to be read back from N-1 or N-2 drived in vdev. It's the same for RAID5. IMHO for identical record/block size RAID5 has no advantage over RAID-Z for reads and does have disadvantage when it comes to small writes. Never mind lack of data integrity checks and other bells and whistles ZFS provides. --Artem
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