Date: Thu, 07 Feb 2008 10:19:38 -0600 From: Eric Anderson <anderson@freebsd.org> To: "fluffles.net" <bsd@fluffles.net> Cc: freebsd-fs@freebsd.org Subject: Re: delayed write buffer Message-ID: <47AB2F9A.8070909@freebsd.org> In-Reply-To: <47A95BC0.1060307@fluffles.net> References: <47A95BC0.1060307@fluffles.net>
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fluffles.net wrote: > Hello kind list, > > I was wondering how to tune FreeBSD's VFS write buffer. I would like a > large amount of RAM (say 500MB out of 1GB) to be reserved or allocated > to be used as write buffer for my backup NAS system. > > If i understand the mechanism correctly, a "dd if=/dev/zero of=/mnt/fs > bs=1m count=500" would act as if i used a malloc-backed md device. This > leads to very nice performance gains, especially in my case because i'm > using encryption causing throughput to be limited to 22MB/s. But if the > first 500MB is free, i can mask this limitation and experience a fast > drive, when writing that is. > > Anyone can point me to the right directions? I tried playing with some > sysctl vfs (notably the vfs.maxmallocbufspace tunable) but did not > achieve the desired effect. And yes, i do know a lot of dirty buffers is > dangerous but my storage setup is redundant enough. Besides i'm just > curious in this topic. :) Could a regular BIO-FLUSH caused by UFS > metadata sync be the curlpit? > > Thanks for any assistance! > Kind greetings, GEOM cache maybe? I can't recall what the status is on it, or what it's real benefits were. I recall it being used for some RAID5 stuff somehow though. Or, how about making a gjournal, with the journal being a MD-backed 'disk'? Eric
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