[Info-vax] Replacement of SCSI tape drives and loaders

[Steven Schweda]

Syltrem wrote:

> QUESTION: Can I do this live ?

   Perhaps.

> My experience (on VAX) is that I can disconnect / reconnect the same drive
> on the VAX and it will not notice, as long as I DO NOT attempt to use the
> drive (do a MOUNT or INIT etc) on it while it is disconnected. Doing so
> would crash the VAX.

   I'd make sure that the whole SCSI bus was idle, not only
the one tape drive.

> QUESTIONS:
> - Should I care about the new drives SCSI addresses ?

   When are you allowed _not_ to care about SCSI IDs?

> - VMS on the ES40 will continue to see the old device (let's say MKA500 if
> the new one replaces MKA400) which is disconnected. If by mistake some
> process tries to access it, will it cause VMS to crash ?

   I believe so.  I doubt it.

> - If I keep the same SCSI address, does it matter if suddenly (as far as VMS
> sees it) the drive model is different ?

   I believe that it will notice the new identity (device
type) when you try to access the new device.  SHOW DEVI /FULL
should provide a clue.

> - The speed of the drive is also different. Without a reboot will VMS make
> the best use of the new unit (the speed of the devices on the bus have
> changed) ?

   Which speed?  SCSI bus speed?  General I/O speed?  What
does VMS know about the speed of the device?

> This is NOT something I've done before so I just don't know.

   Only one way to find out.