Date: Sat, 20 Jun 2009 18:08:35 -0700 From: Kip Macy <kip.macy@gmail.com> To: Erik Trulsson <ertr1013@student.uu.se> Cc: freebsd-fs@freebsd.org Subject: Re: ufs2 / softupdates / ZFS / disk write cache Message-ID: <3c1674c90906201808t1854dd46n82213fbd0c1c254c@mail.gmail.com> In-Reply-To: <20090620231130.GA88907@owl.midgard.homeip.net> References: <cf9b1ee00906201429y7ec68afdse66be30fc2f75e8f@mail.gmail.com> <20090620231130.GA88907@owl.midgard.homeip.net>
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> > My guess is that it will be quite noticable, but that is only a guess. > (Keep in mind that UFS+softupdates does quite a bit of write-caching on its > own, so just switching to ZFS is unlikely to improve write performance > significantly compared to using UFS.) That all depends on how much the drive relies on the write cache for batching writes to disk. Soft updates does a lot of small random writes for metadata updates which will likely be heavily penalized by the absence of write caching. On my SSD, which unfortunately turned out to be camera grade flash, with FFS the system was unusable when doing large numbers of metadata updates, svn checkouts would take hours. I postulated that ZFS would map well to the large erase blocks, so I destroyed /usr and recreated a zpool in its place. I now get random write performance better than FFS, "I lived happily ever after." I don't know if ZFS will provide the same benefit in your situation. My point is just that FFS+SU and ZFS are "apples and oranges." Please note that I've taken -stable off of the the CC, ZFS has been getting a lot of mailing list traffic lately and I've been hearing groans from certain quarters about it drowning out other discussions. Let's try to keep the discussions to freebsd-fs. Thanks, Kip
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