Date: Wed, 09 Mar 2011 15:01:42 +0100 From: Matthias Andree <matthias.andree@gmx.de> To: freebsd-stable@freebsd.org Cc: Jeremy Chadwick <freebsd@jdc.parodius.com> Subject: Re: ZFS performance as the FS fills up? Message-ID: <4D778846.3080008@gmx.de> In-Reply-To: <AANLkTimMct3Ni0p7CBsmNJmW_t6e75mZcHhQ8dppQbCb@mail.gmail.com> References: <BD2C8439-AC1E-49CB-ABE2-9F7F0B292933@punkt.de> <20110308114810.GA37554@icarus.home.lan> <4D775CF1.1010501@gmx.de> <20110309125132.GB62338@icarus.home.lan> <AANLkTimMct3Ni0p7CBsmNJmW_t6e75mZcHhQ8dppQbCb@mail.gmail.com>
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Am 09.03.2011 14:28, schrieb Tom Evans: > On Wed, Mar 9, 2011 at 12:51 PM, Jeremy Chadwick > <freebsd@jdc.parodius.com> wrote: >> >> Otherwise, I can imagine that prefetching could cause what you describe, >> which is enabled by default in 8.0 and 8.1 and auto-disables in 8.2 if >> the amount of available memory is less than 4GB. >> > > I don't think this is accurate. Prefetch was certainly disabled by > default on 8.0 if you had 4GB of RAM or less, requiring the sysctl > vfs.zfs.prefetch_disable=0 to be set if you wanted prefetch and had > 4GB of RAM or less. Personally I've got a 4 GB amd64 setup, had been on RELENG_8 aka 8-STABLE before 8.2-RELEASE (and use RELENG_8_2 aka 8.2-RELEASE now), and I had tried vfs.zfs.prefetch_disable either way without seeing a big difference in sluggish performance (and actually even moved out /usr/home to a UFS file system to get somewhat back up to speed). I suppose that fragmentation was a big issue but cannot confirm that now. However, I cannot produce the data Jeremy has asked for any more, as the incriminated file system no longer exists. I recall ZFS (even the earlier versions before the bigger version leap) was very responsive when it was less than 50% full. I have, however, collected and reformatted (for Wiki) Jeremy's list at <http://wiki.freebsd.org/ZFS/ProblemReporting>; - we'd need to review this and once deemed suitable, link it from the ZFS and possibly ZFSTuningGuide pages, and possibly also from the FreeBSD ZFS manual pages. HTH Matthias -- Matthias Andree
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