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is it STILL not possible to share DLT between servers.

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Steve Post
Trusted Contributor

is it STILL not possible to share DLT between servers.

I saw this in a thread from 2001, that says HP just won't allow it.
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=121886

But is it still not allowed?

I will have two identical rp4440 boxes and a SDLT tape drive in an external box. The drive will be accessable from one box via ultra scsi LVD connection. The second box will not be connected.

I don't see why it can't be connected. But HP told me it's not possible. I would like to really know why. I can see how to do it:

On one box, I will need to change the scsi controller id from 7 to 6.
Then I would plug one cable into boxA, the other end to the tape array box.
I would plug in cable #2 into boxB, and the other to the tape array box.

The scsi adapter on box A would have its controller set to id#7.
The scsi adapter on box B would have its controller set to id#6.
The scsi id of the tape would probably be set to id#5.

I would expect errors if both computers tried to use the tape drive at the same time. I would expect errors if one computer tried to use the tape, while the other computer was off (i.e. no scsi termination). I can easily live with both of those cases. I would just avoid them.

Is there something else that could cause this to fail? Perhaps some type of event monitoring software?

The hardware I'm talking about.....
C7508AZ hp 5300 tape array
2 Hp4440-8 PA8900 computers
A7173A HP Dual Channel Ultra320 scsi adapter
B3920EA hpux OE 11iv1
12 REPLIES
Mike Reznak
Trusted Contributor

Re: is it STILL not possible to share DLT between servers.

Hi,

in OpenVMS we share ESL9000 library with SDLT drives and TZ89 with DLT drives. We use MDMS sw for device locking and everything works just fine.

Mike
...and I think to myself, what a wonderful world ;o)
Steve Post
Trusted Contributor

Re: is it STILL not possible to share DLT between servers.

Well I'm using UNIX, not openVMS. I don't know what MDMS is, but the backup command I would use, would be cpio, or tar, or fbackup.
Mike Reznak
Trusted Contributor

Re: is it STILL not possible to share DLT between servers.

MDMS stands for Media, Device, and Management Services for ABS and HSM.
It's server client software for backup management.
I agree that in Unix world the rules for DLT sharing might be different.
So don't mind my answer.

Mike
...and I think to myself, what a wonderful world ;o)
Steve Post
Trusted Contributor

Re: is it STILL not possible to share DLT between servers.

Thanks for the answers. They don't really apply to me because I'm using a different OS. But at least you gave me the name behind the acronym.

talking rhetorically...

It seems strange I haven't got any more responses. I don't see why it's not possible to hook a tape drive this way. Obviously I would only have the drive used by one server at a time. Obviously I would have 2 different controller id's for the scsi adapter cards. This concept works for disks. I consider a disk much more fragile than a tape. So what gives?


Vincent Fleming
Honored Contributor
Solution

Re: is it STILL not possible to share DLT between servers.

It would probably work just fine, and as you expect, but HP doesn't support that configuration. It's difficult to support.

However, you can do pretty much whatever you want, but expect that any problems would be met with HP support telling you to disconnect the tape drive.

If you want a supported configuration, use Fibre Channel - THAT, we support multi-initiator.

Regards,

Vince
No matter where you go, there you are.
A. Clay Stephenson
Acclaimed Contributor

Re: is it STILL not possible to share DLT between servers.

I have routinely done this for years. It's quite simple although you will have to make sure that only one host is accessing the device at any one time.

Host A (SCSI ID 7 - termination enabled) ------ DLT Drive (SCSI ID 0 or any other free ID) ----- Host B (SCSI ID 6 - termination enabled).

That's all there is too it. You must make certain that you do not exceed the maximum bus length specifications for the SCSI technology that you are using.
If it ain't broke, I can fix that.
Duncan Edmonstone
Honored Contributor

Re: is it STILL not possible to share DLT between servers.

One of HP's engineers (Rick Jones) often posts the following little note on defining 'supported':

Supported, known to work -> warm fuzzies all around
Supported, not known to not work -> an HPite may be in trouble
Supported, known to not work -> an HPite is in trouble
Unsupported, known to work -> lucky today, unlucky tomorrow?
Unsupported, not known to not work -> there but for the grace of Turing
Unsupported, known to not work -> no, it was not deliberate ;-)

So go for it, but have a method of reconfiguring to a supported config before you expect any help from HP...

HTH

Duncan

HTH

Duncan
Duncan Edmonstone
Honored Contributor

Re: is it STILL not possible to share DLT between servers.

...and of course the *ironic* thing about this is that if you bought a FC switch, HBAs and a NSR (FC-SCSI Bridge), then HP *would* support you with 2,3,4 or more hosts of differing architecture and OS all seeing the tape drive, although in my opinion this is a far more complex and 'difficult to support' configuration.

Nobody ever said life was fair.

Duncan

HTH

Duncan
Steve Post
Trusted Contributor

Re: is it STILL not possible to share DLT between servers.

I'll try network backups first. But it would be nice to just wire it up.

I've been reading HP's "SCSI Solutions White Paper HP-UX June 15, 2005". "Shared SCSI bus -targets: The only target devices allowed on a shared SCSI bus are disk devices, including disk arrays. No tape drives, CD-ROMs, Magneto-Optical disks, or scanners are allowed on a shared SCSI bus in HP-UX."
A. Clay Stephenson
Acclaimed Contributor

Re: is it STILL not possible to share DLT between servers.

The method I showed you is actually a very neat way to configure tape drives under DP. I use the logical drive attached to the database server for the backups and then use the logical device attached to my Cell Server to make the copies of the backups during the day. That way the database server is not loaded during the day while the copies are underway. I've used this configuration on many tape drives under OB2/DP2 for > 6 years w/o a single problem --- and yes, Mr. HP Goodwrench has been onsite to replace drives w/o a single complaint.
If it ain't broke, I can fix that.
Stuart Whitby
Trusted Contributor

Re: is it STILL not possible to share DLT between servers.

The reason they don't want mixed media types on the same bus is probably because of SCSI resets. Some devices handle them without problem, some don't. Specifically, if a disk gets a reset during a write, the response doesn't come back, the head is pointed at the right point on disk again and the block is written correctly. A reset on tape will rewind the tape to the beginning, at which point it will keep writing (being a serial device) and overwrite whatever you've already written.

Shouldn't be a problem to cable though. Set up for SCSI reserve as well - tells you in SAM (sts_....something or other)
A sysadmin should never cross his fingers in the hope commands will work. Makes for a lot of mistakes while typing.
Tom Pojatina
Occasional Visitor

Re: is it STILL not possible to share DLT between servers.

Hi Steve:

I might have a device which will solve your troubles by allowing you to connect multiple systems (in your case) 2 host sustems to the SDLT. It is called the Omni64 from LXI Corp an HP Development Partner http://lxicorp.com/partnersdp.htm .

If you have interest please feel free to contact myself. The PDF that I have pertaining to the box is over 1MB and unfortunately it is unable to be attached.

Regards,
Tom