Date: Tue, 5 Mar 2002 12:55:30 -0800 (PST) From: Julian Elischer <julian@elischer.org> To: Zhihui Zhang <zzhang@cs.binghamton.edu> Cc: freebsd-hackers@freebsd.org Subject: Re: A weird disk behaviour Message-ID: <Pine.BSF.4.21.0203051255050.26829-100000@InterJet.elischer.org> In-Reply-To: <Pine.SOL.4.21.0203051527280.10139-100000@onyx>
next in thread | previous in thread | raw e-mail | index | archive | help
more writes fit in the disk's write cache? On Tue, 5 Mar 2002, Zhihui Zhang wrote: > > I am doing some raw I/O test on a seagate SCSI disk running FreeBSD 4.5. > This situation is like this: > > +-----+----+----+----+----+----+----+----+----+----+---+------ > | | | | | | | | | | | | .... > +-----+----+----+----+----+----+----+----+----+----+---+------ > > Each block is of fixed size, say 8192 bytes. Now I have a user program > writing each contiguously laid out block sequentially using /dev/daxxx > interface. There are a lot of them, say 15000. I write the blocks in two > ways (the data used in writing are garbage): > > (1) Write each block fully and sequentially, ie. 8192 bytes. > > (2) I still write these blocks sequentially, but for each block I only > write part of it. Exactly how many bytes are written inside each block is > determinted by a random number between 512 .. 8192 bytes (rounded up a > to multiple of 512 bytes). > > I find out the the performance of (2) is several times better than the > performance of (1). Can anyone explain to me why this is the case? > > Thanks for any suggestions or hints. > > -Zhihui > > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hackers" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.BSF.4.21.0203051255050.26829-100000>