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From: jgh@gec-mi-at.co.uk (Jeremy Harris)
Newsgroups: net.unix-wizards
Subject: Re: disk partitioning
Message-ID: <235@miduet.gec-mi-at.co.uk>
Date: Mon, 22-Sep-86 08:45:50 EDT
Article-I.D.: miduet.235
Posted: Mon Sep 22 08:45:50 1986
Date-Received: Tue, 23-Sep-86 03:55:47 EDT
References: <7247@sun.uucp>
Sender: jgh@gec-mi-at.co.uk
Reply-To: jgh@gec-mi-at.co.uk (Jeremy Harris)
Organization: Marconi Instruments Ltd., St. Albans, Herts, UK
Lines: 19
Keywords: SCSI bad blocks

In article <7247@sun.uucp> mojo@sun.UUCP (Joseph Moran) writes:
>`SCSI' disks (ST506 and ESDI) let the controller handle forwarding bad
>blocks.  The good side of this is that the UNIX driver should always
>see a perfect disk.  The down side of this is that a bad sector which
>shows up after the original format of the disk can only be "mapped out"
>by using a disk utility to reformat the entire disk.

	The SCSI spec defines an optional command 'reassign blocks' for
normal and WORM disks.

>`SMD' disks (e.g. A "normal" Fujitsu eagle) *CAN* let the controller
>handle the bad block forwarding, but you have more control.  The
>controller can avoid a bad block by "slipping" a sector.  When this
>happens normally a logical sector is slipped to a spare sector on the
>same track.  This way the data is on the same cylinder and track that
>the file system expected.

	Some SCSI controllers do forwarding this way too. There's nothing
in the SCSI spec which says where the replacement blocks have to be.

Jeremy Harris	jgh@gec-mi-at.co.uk	...!mcvax!ukc!hrc63!miduet!jgh