topic Re: Two tape drives, one SCSI interface in Operating System - HP-UX

Two tape drives, one SCSI interface

Fred Martin_1 — Thu, 16 Jul 2009 17:23:14 GMT

Up to now I've had one DLT7000 tape drive C6375A. It's been in a 3U Rack Mount, C4318B. The other half of the rack has been empty.

The tape drive is the only device on a SCSI interface.

I've decided that I need to have two drives, one as a spare. I'd like to be able to switch drives regularly, just as a confidence test that both drives still work.

So I got another C6375A DLT. I mounted it the rack next to the other. Gave the new one it's own SCSI address.

Now, I'm sure it's a bad idea to put both drives on the same chain, for performance reasons. It's not my intention to use both drives at the same time.

But other than that, can they live together on the same chain, as a convenience for me?

I'm thinking that I could just power on the drive I want to use that week, and leave the other powered off.

Just want to see if this is a bad idea.

As an alternative I could give both devices the same address and physically swap them each week, but I'm trying to avoid that.

Thoughts pls.

Re: Two tape drives, one SCSI interface

Mel Burslan — Thu, 16 Jul 2009 17:33:24 GMT

As long as the two drives have different scsi numbers, there is nothing wrong with leaving both of the powered on (of course green activists will beg to differ here {grin}), hanging off the same scsi interface. As long as you are not running both of them at the same time, there aren't any performance penalties on the unit which is being utilized.

So go ahead and do it.

Re: Two tape drives, one SCSI interface

Fred Martin_1 — Thu, 16 Jul 2009 17:46:49 GMT

I don't have to worry about powering the drives up/down while the server is up, do I?

Re: Two tape drives, one SCSI interface

OldSchool — Thu, 16 Jul 2009 17:47:11 GMT

sure it will work, as long as the interface is the same (and since their the same model I'd assume they are) and the scsi addresses are different, and the last one in the chain is properly terminated.

Re: Two tape drives, one SCSI interface

OldSchool — Thu, 16 Jul 2009 17:50:28 GMT

"I don't have to worry about powering the drives up/down while the server is up, do I?"

if you're talking for installation, its probably better to shutdown the system.

after installation, I'd leave the drives "up" all the time.

Re: Two tape drives, one SCSI interface

Mel Burslan — Thu, 16 Jul 2009 17:56:07 GMT

Agree with OldSchool here. Powering the drives up and down may send some bad signalling to the system, causing unstability. I'd keep bot drives on, 24x7 if I were you.

Re: Two tape drives, one SCSI interface

Steven E. Protter — Thu, 16 Jul 2009 18:27:50 GMT

Shalom,

HP recommends one tape drive per scsi card.

If you use both drives at the same time, performance may significantly degrade.

Source: HP Response Center, 2002 response center call I was on.

Yes. I remember.

SEP

Re: Two tape drives, one SCSI interface

Fred Martin_1 — Thu, 16 Jul 2009 18:28:34 GMT

Thanks folks. I think I'm all set now.

Re: Two tape drives, one SCSI interface

Steven Schweda — Thu, 16 Jul 2009 20:57:52 GMT

> I'd keep bot drives on, 24x7 if I were you.

I'd avoid changing the power state of any
device on the bus while any other device on
the bus is busy. I normally cycle the power
daily on a DLT4000 on my Alpha (VMS) system
with no ill effects.

> sure it will work, as long as [...]

And the cable's not too long.