Date: Tue, 18 Nov 1997 04:31:04 -0500 (EST) From: "John S. Dyson" <toor@dyson.iquest.net> To: reyesf@super.zippo.com Cc: hackers@FreeBSD.ORG Subject: Re: Optimizing HD I/O. What size to use to read/write? Message-ID: <199711180931.EAA01111@dyson.iquest.net> In-Reply-To: <199711180759.XAA20331@super.zippo.com> from Francisco Reyes at "Nov 18, 97 02:59:09 am"
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Francisco Reyes said: > I am going to start working on a program which will be heavy on I/O. > I was wondering what would be a good size to read/write at a time. > > What is the minimun block size FreeBSD allocates? 4K? 8K? Is it HD > dependent? > Depends on the filesystem configuration. On a 8K filesystem with 1K fragments, the filesystem will normally allocate 8K blocks, except for the last one, which will be some number of fragments. The kind of I/O dictates the blocksize that you want to use. There is generally little use of using more than a (8K:1K or 16K:2K) filesystem. The clustering code takes care of changing small sequential transfers into larger (up to 64K for now) device I/O. If you are talking about random I/O, in a database type situation, you might want to bypass filesystems all together. -- John dyson@freebsd.org jdyson@nc.com
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