[comp.unix.ultrix] Bad Block Forwarding?

steve@avalon.dartmouth.edu (Steve Campbell) (08/23/89)

Does Ultrix 3.1 (RISC) perform automatic bad block forwarding (revectoring)
on SCI disks such as RA90's?  What strategy is used?  Does anything prevent
runaway forwarding in the instance of false bad block errors that are caused
by other electronic failures?
							Steve Campbell
							Dartmouth College

alan@shodha.dec.com ( Alan's Home for Wayward Notes File.) (08/23/89)

In article <15164@dartvax.Dartmouth.EDU>, steve@avalon.dartmouth.edu (Steve Campbell) writes:
> Does Ultrix 3.1 (RISC) perform automatic bad block forwarding (revectoring)
> on SCI disks such as RA90's?  What strategy is used?  Does anything prevent
> runaway forwarding in the instance of false bad block errors that are caused
> by other electronic failures?
> 							Steve Campbell
> 							Dartmouth College

	Well first the RA90 isn't a SCSI disk.  In V3.0 and V3.1
	the SCSI support doesn't include dyanmic BBR.  There is a
	program called rzdisk that will let you do this by hand.
	I wouldn't be suprised if a future version supports dynamic
	BBR in the SCSI drivers.

	The DECsystem 5400 and 58xx, which run V3.1, use the KDA50,
	KDB50, HSCxx and other DSA controllers do support dynamic
	BBR.  The exact stratagy varies from disk to disk, but on
	most of the disks there is one extra sector per track that
	is used for revectoring.  Some disks may have more than one.

	Except for the time I tried to use an RD52 that was unformatted
	I've never seen "runaway BBR".  I don't know if there is anything
	built into the algorithms to watch for this, but in the worst
	case the control tables on the disk will fill up or become
	corrupted you'll see messages like:

		Unit x write protected.  Backup media and reformat.

	I don't remember if this was catastrophic electronic failure
	or a head crash, when it happened to me.  There weren't that
	many blocks that had been revectored, though.
-- 
Alan Rollow				alan%nabeth.dec.com@decwrl.dec.com

steve@avalon.dartmouth.edu (Steve Campbell) (08/24/89)

In article <388@shodha.dec.com> alan@shodha.dec.com ( Alan's Home for Wayward Notes File.) writes:
>In article <15164@dartvax.Dartmouth.EDU>, steve@avalon.dartmouth.edu (Steve Campbell) writes:
>> Does Ultrix 3.1 (RISC) perform automatic bad block forwarding (revectoring)
>> on SCI disks such as RA90's?  
       ^
Sorry, I fat-fingered that.  I meant to say SDI (Standard Disk Interconnect?).
My understanding is that disks using SDI also use the Mass Storage Control
Protocol and are controlled by the UDA/KDB family of controllers.  As Alan
says, the answer to my question is yes.  Thanks.
							Steve