Date: Thu, 12 Nov 2009 22:28:55 +0100 From: Ivan Voras <ivoras@freebsd.org> To: Scott Ullrich <sullrich@gmail.com> Cc: freebsd-current@freebsd.org Subject: Re: Help ZFS FreeBSD 8.0 RC2 Write performance issue Message-ID: <9bbcef730911121328t342b2268oceba3712b52511d4@mail.gmail.com> In-Reply-To: <d5992baf0911121314k7f535f2cra2d3e8367774d8ca@mail.gmail.com> References: <11167f520911111050j36dd94far667c81e6f5c18e69@mail.gmail.com> <20091111204903.GI89052@dan.emsphone.com> <11167f520911111326v13bb442bt36e853afbecdf834@mail.gmail.com> <9bbcef730911111352t12188bdajbca71bcf35a5beb5@mail.gmail.com> <Pine.GSO.4.63.0911121147310.9126@muncher.cs.uoguelph.ca> <11167f520911121044l74744c30u5a4d9ca008ab863c@mail.gmail.com> <d5992baf0911121048o76c1543el2b4d9de84ffb107@mail.gmail.com> <11167f520911121101o403751ddmb544dfaf1c61bf1e@mail.gmail.com> <ed91d4a80911121219sa0f3fa3s934791725028a966@mail.gmail.com> <d5992baf0911121314k7f535f2cra2d3e8367774d8ca@mail.gmail.com>
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2009/11/12 Scott Ullrich <sullrich@gmail.com>: > On Thu, Nov 12, 2009 at 3:19 PM, Artem Belevich <fbsdlist@src.cx> wrote: >> >> Log seems to be somewhat weak point in ZFS. If you lose your log >> device, you will lose your pool. Plus, there's no way to remove log >> device from the pool. So, once you attach some device as a log, you'd >> better be sure that device does not disappear, because it will take >> the rest of the pool with it. From that point, real ram-disk (i.e. >> /dev/mdN) is definitely a recipe for disaster. External ramdisk with a >> battery backup may be an option, but even in mirrored configuration >> seems rather risky to me. >> >> http://jmlittle.blogspot.com/2008/05/problem-with-slogs-how-i-lost.html >> >> I'd say that SSD are probably the best fit for slog role. > > Indeed. =C2=A0 I mirrored 2 SSDs on an Areca in case I loose one of them. > Partitioned the SSD into a log device and the rest being cache (see > the ZFS best practices guide for details). > > Needless to say my performance matches that of normal writes and reads > when using NFS now. So in short, you are saying the to get "normal" performance out of ZFS+NFS, the best way is to invest in an Areca and 2 SSDs :))
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