Date: Fri, 5 Jan 2007 12:31:27 +0100 From: lulf@stud.ntnu.no To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: freebsd-current@freebsd.org, freebsd-geom@freebsd.org Subject: Re: Pluggable Disk Schedulers in GEOM Message-ID: <20070105123127.gnk0v58p44488g48@webmail.ntnu.no> In-Reply-To: <3763.1167992304@critter.freebsd.dk> References: <3763.1167992304@critter.freebsd.dk>
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Siterer Poul-Henning Kamp <phk@phk.freebsd.dk>: > In message <20070105015800.s3rqdzgm8k8owk4s@webmail.ntnu.no>, =20 > lulf@stud.ntnu.no > writes: > >> I was wondering if someone have started on the pluggable >> disk-scheduler project >> on the "new ideas"-page yet. >> >> I was thinking on how one could implement this in GEOM by [...] > *snip* > > Here are some ideas: > > Remove disksorting and see if if and how big a difference > it makes today. Test both SCSI, ATA and USB media, and > test both low-level benchmarks and "real-world" workloads. > > Change disksorting to reverse unidirectional elevator > and bidirectional elevator and see if it makes a difference. > (Modern disks store blocks in reverse sector order on > the disk, discover and explain why) > > Capture an I/O trace from a suitably sensible realworld > system, including the detailed timestamps of issuance > and completion of the requests. Treat results statistically > and try to determine a formula for predicting how long > a given request is going to take for the disk. > > It's not that I think that all your ideas are bad, I am just > not sure that the (traditional) view of the hardware they > are based on, is still relevant, and I think your time would > be much better spent addressing that question. > I understand, and I clearly see the point about new hardware being =20 more intelligent in these matters. However, I will look into this a bit more just out of curiosity, and =20 do some actual test on how this can affect performance in the =20 scenarios you describe. And thanks for the tips! --=20 Ulf Lilleengen
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