Date: Thu, 31 Aug 1995 10:07:21 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: rgrimes@gndrsh.aac.dev.com (Rodney W. Grimes) Cc: pete@kesa26.kesa.com, jbryant@argus.iadfw.net, freebsd-hackers@FreeBSD.ORG, pete@rahul.net Subject: Re: 4GB Drives Message-ID: <199508311707.KAA22925@phaeton.artisoft.com> In-Reply-To: <199508311257.FAA11224@gndrsh.aac.dev.com> from "Rodney W. Grimes" at Aug 31, 95 05:57:14 am
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> Now, can you all leave me alone for 30 days so I can go get the stripes > working, I have small bottleneck that needs fixed :-):-):-) And can > anyone tell me what the mean and standard deviation of an I/O request to > an aic7870 is before it hits the drive given 0 scsi bus contention? This > seems to greatly effect rotation offset on stripe sets when pushed to > the limits of data coming under the head just after the I/O hits the > drive. Modern drives write sectors in reverse order; when asked to read, they start reading from where the head is at and keep reading until the sector you want is read. For contiguous reads, this pre-caches the data. I think you would achieve an effect opposite of the one you want if you were to successfully rotdelay. One thing that *would* speed you up is not crossing physical cylinder boundries (seek scheduling ala the old BSD code). The problem with this is that the information is only available from SCSI II devices and is not linearly bound (ie: the track length varies by zone), making it difficult to use without adding a lot of overhead. But it's probably yor best bet. Without the physical seek locations, any benchmarking will be rather arbitrary based on the layout you end up with for a particular test. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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