Date: Wed, 3 Apr 1996 11:50:08 +0200 (MET DST) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: msmith@atrad.adelaide.edu.au (Michael Smith) Cc: msmith@atrad.adelaide.edu.au, bde@zeta.org.au, davidg@Root.COM, dutchman@spase.nl, freebsd-hackers@FreeBSD.ORG Subject: Re: HDD cpu usage (IDE vs. SCSI). Message-ID: <199604030950.LAA01500@labinfo.iet.unipi.it> In-Reply-To: <199604030906.SAA19932@genesis.atrad.adelaide.edu.au> from "Michael Smith" at Apr 3, 96 06:36:15 pm
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> Luigi Rizzo stands accused of saying: > > Ah, so you want the system to know how each and every drive works, and > to keep track of actuator position and velocity, as well as the rotational > position of the media. Funny ha ha. > The only part of the system in a position to make an _informed_ decision > about which of several transactions is the easiest to perform next > is the disk. With ZBR, hidden geometry and 'invisible' sector sparing, > the OS doesn't have a hope. (Yes Terry, I know, RAID-X) Agree. I wanted to mention this but forgot while writing the reply. Actually this raises the question of for how long the fs code will need or even benefit from trying to arrange data in a contiguous fashion (cylinder groups, log fs etc.). It is right that disks tend to hide features from the disk, but a bit of cooperation is certainly useful (as a minimum, I should be able to tell the disk "this block is likely to be accessed sequentially after block X"). One last thing, with "invisible" sector sparing it's probably the user who doesn't have a hope, but this ought to be an infrequent occurrence. Luigi ==================================================================== Luigi Rizzo Dip. di Ingegneria dell'Informazione email: luigi@iet.unipi.it Universita' di Pisa tel: +39-50-568533 via Diotisalvi 2, 56126 PISA (Italy) fax: +39-50-568522 http://www.iet.unipi.it/~luigi/ ====================================================================
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