Date: Wed, 06 Feb 2008 08:03:28 +0100 From: "fluffles.net" <bsd@fluffles.net> To: freebsd-fs@FreeBSD.org Subject: delayed write buffer Message-ID: <47A95BC0.1060307@fluffles.net>
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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, Veronica
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