Date: Thu, 12 Nov 2009 12:19:39 -0800 From: Artem Belevich <fbsdlist@src.cx> To: "Sam Fourman Jr." <sfourman@gmail.com> Cc: Rick Macklem <rmacklem@uoguelph.ca>, Dan Nelson <dnelson@allantgroup.com>, Ivan Voras <ivoras@freebsd.org>, freebsd-current@freebsd.org, Scott Ullrich <sullrich@gmail.com> Subject: Re: Help ZFS FreeBSD 8.0 RC2 Write performance issue Message-ID: <ed91d4a80911121219sa0f3fa3s934791725028a966@mail.gmail.com> In-Reply-To: <11167f520911121101o403751ddmb544dfaf1c61bf1e@mail.gmail.com> References: <11167f520911111050j36dd94far667c81e6f5c18e69@mail.gmail.com> <hdf23m$b6n$1@ger.gmane.org> <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>
next in thread | previous in thread | raw e-mail | index | archive | help
> is there anyway to safely have a log device on a ramdisk? I would assume not. 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. --Artem
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?ed91d4a80911121219sa0f3fa3s934791725028a966>