Date: Wed, 10 Jan 2007 12:57:02 +0100 (CET) From: Oliver Fromme <olli@lurza.secnetix.de> To: freebsd-stable@FreeBSD.ORG, ghelmer@palisadesys.com Subject: Re: 6.x loosing record of free space after filesystem fills? Message-ID: <200701101157.l0ABv2qq089648@lurza.secnetix.de> In-Reply-To: <45A3E3B9.4030205@palisadesys.com>
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Guy Helmer wrote: > Oliver Fromme wrote: > > Why are you using those blocksize and fragsize settings? > > (If you store large files, then you should at least also > > decrease the inode density, using the -i option.) > > > These settings were chosen to optimize I/O throughput for Postgresql on > the theory that a 64KB block size would maximize disk throughput in the > general case (especially for a RAID 10 system) and an 8K frag size would > match Postgresql's page size. I don't think that that theorie holds true in reality. Did you perform any benchmarks to verify it? In fact, I would expect the performance to be better when using a block size of just 8KB and a frag size of 1 KB. By the way, this is an excerpt from the tuning(7) manpage: | FreeBSD performs best when using 8K or 16K file system block | sizes. The default file system block size is 16K, which provides | best performance for most applications, with the exception of | those that perform random access on large files (such as database | server software). Such applications tend to perform better with | a smaller block size, although modern disk characteristics are | such that the performance gain from using a smaller block size | may not be worth consideration. Using a block size larger than | 16K can cause fragmentation of the buffer cache and lead to | lower performance. Guy Helmer wrote: > I wasn't aware of any known regressions in 6.x regarding large > filesystem block sizes... I'm not aware of any regressions either. 64 KB bsize and 8 KB fsize didn't work reliable in 4.x, and the situation doesn't seem to have gotten worse (maybe it has gotten better with UFS2, but I didn't perform extensive tests with it because the non-standard bsize/fsize pessimize performance anyway). Best regards Oliver -- Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd Any opinions expressed in this message may be personal to the author and may not necessarily reflect the opinions of secnetix in any way. "That's what I love about GUIs: They make simple tasks easier, and complex tasks impossible." -- John William Chambless
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