Date: Mon, 28 Mar 2011 07:32:29 -0700 From: Freddie Cash <fjwcash@gmail.com> To: Claus Guttesen <kometen@gmail.com> Cc: FreeBSD Stable <freebsd-stable@freebsd.org> Subject: Re: zfs, nfs and zil Message-ID: <AANLkTimOjxS12fgWnp2QHaJsb5ixKdFXtfvM2i0JdLH6@mail.gmail.com> In-Reply-To: <BANLkTinZvLDkmUNHmDGQpQFRr31s=hyHuQ@mail.gmail.com> References: <BANLkTinZvLDkmUNHmDGQpQFRr31s=hyHuQ@mail.gmail.com>
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On Mon, Mar 28, 2011 at 4:22 AM, Claus Guttesen <kometen@gmail.com> wrote: > I've setup a server with FreeBSD 8.2 (prerelase) and patched zfs to > ver. 28. The server has 11 disks each 2 TB in raidz2. The performance > is very good and I've got approx. 117 MB/s on plain GB nics using > iscsi. > > I'm mounting the FreeBSD-server from a couple of vmware esxi 4.1 > servers using nfs, but when there is alot of i/o the server becomes > unresponsive, easily triggered by installing ie. ms-sql. The server > itself is up but is not reachable from the network. When I take the > nic down and up again connection to the network is reestablished > (ip-wise). > > A friend of mine has suggested that I disable the zil. The page > http://wiki.freebsd.org/ZFSTuningGuide says 'Disabling ZIL is not > recommended where data consistency is required (such as database > servers) but will not result in file system corruption.' > > Has anyone tried to disable zil and achieved better performance and > still maintain a consistent filesystem? If your disk controller has a lot of cache on it, and a battery backup, then enabling the write cache and disabling the ZIL can be faster, without sacrifising consistency (the write cache on the controller acts like a ZIL). There's several threads on the zfs-discuss mailing list where this is discussed. However, the better solution, and the one most recommended for those using NFS with ZFS, is to install a small, write-optimised, SLC-based SSD to the system as a separate log (SLOG/ZIL) device. NFS is a very sync-heavy protocol, and having a super-fast ZIL sitting on a separate SSD will greatly improve things. -- Freddie Cash fjwcash@gmail.com
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