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Conference spezko::cluster

Title:	+ OpenVMS Clusters - The best clusters in the world! +
Notice:	This conference is COMPANY CONFIDENTIAL. See #1.3
Moderator:	PROXY::MOORE

Created:	Fri Aug 26 1988
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	5320
Total number of notes:	23384

5305.0. "Tape Library Robot on shared SCSI bus?" by BIGCHZ::EZZELL (Mike Ezzell) Wed May 07 1997 21:11

I have read the notes stating why tape drives are not supported on shared
SCSI buses.  

Is there a reason for not supporting a tape library robot by itself on a 
shared SCSI bus?  I am configuring a TL896 in a cluster and it would be great
if the robot controller could be on a shared SCSI bus.

T.R	Title	User	Personal Name	Date	Lines
5305.1	Some things to consider....	STAR::CROLL		`Thu May 08 1997 10:33`	16
	Can the jukebox driver software deal with two instances of the robot control software dealing with the same robot? Most of the time, the robot control software can't....so you have no failover capability. Also, unless the robot driver can deal with port allocation classes, there's no way to have the same device name on the nodes at either end of the SCSI bus. The code that deals with port allocation classes only knows about tapes and disks. Is this OSMS or something else you're speculating about? I don't think OSMS can deal with this; hopefully Rob Seneker will chime in with his opinion. John
5305.2	SCSI Resets Affect Tapes More Than Disks...	XDELTA::HOFFMAN	Steve, OpenVMS Engineering	`Thu May 08 1997 10:52`	11
	In addition to John's comments around coordination of access, one also has to determine if the robot controller can deal with SCSI resets in a desirable fashion -- tapes usually react by rewinding and resetting, which is not necessarily desirable behaviour in a shared environment. As an (ugly) option here, consider using a SCSI switch. (This is not even a good solution, but it does avoid the recabling usually needed when swapping widgets between two SCSI busses, and it does avoid the problems with the SCSI resets.)
5305.3	Discussion in ASK_SSAG	BIGCHZ::EZZELL	Mike Ezzell	`Thu May 08 1997 11:22`	5
	I just discovered an ongoing discussion in the ASK_SSAG notes file on the effects of a SCSI bus reset on tape library robots. This effect appears to be undefined at this time.