Sharing DLT with 2 servers?

[Joel Shank]

Hi All

Does anyone know if I can daisy-chain two DLT tape drive together, where one DLT is attached to HOSTA and the other is attached to HOSTB.

If the SCSI IDs are set so there is no conflict, can this be done so both servers can see and use both tape drives?

This seems like it would work (similar to Service Guard).

Has anyone tried this? Does anyone know why it would NOT work?

Thanks in advanced,
JLS

[Rita C Workman]

Are you meaning can you take 1 DLT tape library that has 2 drives and connect each tape drive to a different server????

If that's the question, the answer is YES.

/rcw

[Kofi ARTHIABAH]

Joel:

I do not think it will work - you are considering setting up two adapter/controllers (servers) on a single SCSI bus - there can only be one SCSI adapter/controller (and terminator) on a SCSI chain... otherwise, there would be contention for signals sent down the wire.


what you could do is to put both on one server and remotely use them from the second server.

[Patrick Wallek]

I saw a post at some point where someone wanted to share a device between 2 servers, an AutoRaid I think. The point that one of the respondants made was that you would need to change the SCSI ID of the SCSI controller on one of your boxes so that you don't wind up with two devices (ie. controllers) on the same SCSI chain with the same SCSI ID. I can see where that would cause problems.

If your setup was something like the following, it may work. No promises though.


Server A (SCSI Controller ID 7)<-->DLT Drive1 (SCSI ID 6)<-->DLT Drive2 (SCSI ID5)<-->Server B (SCSI ID 4)

[Joel Shank]

I am not using a library. I am using standalone DLT tape drives.

How does Service Guard get around the one controller on a SCSI chain? Isn't this how SG works -- HOSTA is attached to a disk and HOSTB is attached to the same disk.

What I am trying to do is the same this only use tape drives instead of disks.

Any thoughts?

JLS

[Tracey]

If there is a one to one relationship for physical connection to a server (DLT1 on HP1, DLT2 on HP2). Then you can simply go into SAM and export the tape drives for accessing by the other machine, and then import the drive on the other. They tape drives will have two diffrent names of course, but then they will be able to be used by either system.

[Joel Shank]

The problem I have with attaching one of the drives remotely is there is potentially a hugh amount of data that will be backed up, and I would like to have the drive attached directly.

I just looked at my Service Guard servers and both servers have their respective SCSI initiator ID set to 7. I am confused, from what I am being told, wouldn't this cause a SCSI conflict? Or is it because the volume group they share is inactive on one server while active on the other? (Just thinking out load)

If I need to, how would I go about changing the iniiator's SCSI ID? I thought it was "hardcoded" to 7.

I really appreciate everyone's help. And I will be assigning points. :-)

JLS

[Patrick Wallek]

Here is the link to the thread I mentioned earlier where a person is wanting to connect two L1000 machines to a single AutoRaid 12H array.

A couple of the responses talk about how to go about changing the SCSI ID of the controller.

http://forums.itrc.hp.com/cm/QuestionAnswer/1,1150,0x37ac14a24fd1d4118fef0090279cd0f9,00.html

I hope this helps.

[Tracey]

My NT network guy just told me that there is a SCSI sharing device you can purchase from a company called BlackBox - I am sure there are other companies too.

[Dave Wherry]

It can be done and here's how I do it. It requires fibre channel interfaces on your hosts.
Each host has a fibre channel interface. These are connected to a FC/SCSI Multiplexor (A3511A). Then on the back side of the multiplexor there can be up to 4 SCSI interfaces. Connect these to your tape drives.
Each host sees both tape drives. I am using it with 2 DLT libraries, each having 2 DLT8000 drives. In my case each host sees both libraries, 40 tapes, and all 4 drives. Gives me a lot of flexibility in scheduling and running my backups.

[Tim Malnati · Accepted solution]

It is relatively simple at the hardware level to share a scsi device between multiple hosts. The scsi id on at least one host must be changed though. It is better if you change the scsi id on both hosts however. Say move one from 7 to 6 and the other from 7 to 5 (each scsi id must be unique on a bus). The idea here is that if someday you have a problem with one of your controllers and your friendly CE comes to change it, he just might not notice that the id has been changed from default and reinstall a new card back to id 7. If they are both changed initially, his error won't cause an additional problem (Murphy's law says the one changed will be the one that fails).

The issue that still remains is how do you control things to make sure that both machines don't attempt to use the same device at the same time? There are a variety of methods of doing this (lock file flags, etc). My guess is that the OS would complain if it found the device busy (but I'm not sure how it would handle it). But there is the posibility that the device might not necessarily be busy all the time during an evolution (for example a tape change). The bottom line is that some form of locking scheme will be needed.