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From: grandi@noao.UUCP (Steve Grandi)
Newsgroups: net.unix-wizards
Subject: Re: disk partitioning
Message-ID: <497@carina.noao.UUCP>
Date: Fri, 12-Sep-86 23:58:23 EDT
Article-I.D.: carina.497
Posted: Fri Sep 12 23:58:23 1986
Date-Received: Sat, 13-Sep-86 09:50:51 EDT
References: <3496@brl-smoke.ARPA> <385@brueer.ee.brunel.ac.uk>
Reply-To: grandi@noao.UUCP (Steve Grandi)
Organization: Natl. Optical Astronomy Observatories, Tucson, AZ USA
Lines: 20

In article <385@brueer.ee.brunel.ac.uk> andrew@me.brunel.ac.uk (Andrew Findlay) writes:
>Sort of.. The disk driver (/sys/vaxuba/uda.c in your case) will map any
>bad sectors to the appropriate replacement sectors on both the source and
>destination disks. Thus, the disks appear to be perfect until you reach
>the bad sector table itself. This is on the last track, which is usually
>defect-free anyway. Once you start copying this, the destination disk's
>bad sector info gets overwritten with that from the source disk. Even now,
>things will be OK - UNTIL YOU REBOOT THE SYSTEM. The duff bad-sector info
>will then be picked up and all hell will break loose.
>
For UDA-50 supported disks (i.e. RA81s) this is INCORRECT.  They DO NOT
have bad-block tables that can be accessed by normal disk read/writes.
Their bad block forwarding is done by the hardware using spare sectors
thoughtfully provided in each track.  Other tables used in the revectoring
process itself are also inaccessible by normal reads and writes.  
In short, it is safe to use the entire RA81 disk (all 891072 sectors) without 
worrying about bad block tables.
-- 
Steve Grandi, National Optical Astronomy Observatories, Tucson, AZ, 602-325-9228
{arizona,decvax,hao,ihnp4,seismo}!noao!grandi  grandi%draco@Hamlet.Caltech.Edu