DPM Tape Backup Troubleshooting

While recently setting up tape library sharing in DPM 2012 in an enterprise class environment I ran into several snags. So let’s explore those hurdles and how we can overcome them!

But before we dive into the fun lets get some acronyms out of the way:

  • LCS (Library Control Server) server: the only DPM server that controls the medium changer. This server also shares its tape configuration with the LTC.
  • LTC (Library Tape Client): Any DPM server that connects to the LCS. It asks the LCS to handle media on it’s behalf.

First Steps
Run through ALL the steps listed in this great article:

https://blogs.technet.com/b/dpm/archive/2011/12/20/how-to-troubleshoot-tape-library-sharing-configuration-issues-in-dpm-2010.aspx

EXCEPT the last one as you really should not have to move the LCS to a new host. If you’re at that point, you should just rebuild the LCS.

Issue One
First problem is how do you make one tape library accessible to many DPM servers? Tape library sharing! While this is a good attempt to make tape backups work in an enterprise, it comes with it’s share of problems. So assuming you’ve followed the instructions at https://technet.microsoft.com/en-us/library/hh758124.aspx you should have a working library right? No! Now onto problem 2.

Issue Two
The link above doesn’t make any mention of SAN zoning other than “The tape library must be in a storage area network (SAN) environment.” Well, this is a bit misleading and what does it really mean? Also, how about multi-pathing, how is that handled? So let’s break it down:

  1. If the tape library has a separate WWN for the robotics, then use it! This allows the zoning of only the robotics or media changer to the LCS and the drives to the LTC.
  2. If the tape library does not have separate WWNs for the media changer and drives then you will have to take note of section 2 “Check the Medium Changer in Device Manager” https://blogs.technet.com/b/dpm/archive/2011/12/20/how-to-troubleshoot-tape-library-sharing-configuration-issues-in-dpm-2010.aspx. Since the LTC can see the media changer, you need to be sure to disable the media changer device so that TLC cannot communicate with the media changer.
  3. The MPIO feature built into Windows can combine multiple paths for SAN devices, however, this does not work for tape drives. If you do both, then the OS will see 1 drive as two separate drives and you will have a mess in DPM. So you can only zone the drives and robotics on one path.

Issue Three
Even after getting tape library sharing to work and setting the auto refresh to the minimum five minutes, there are still time when the library does not show in the GUI. From my understanding this can happen when two LTCs access the TLS at the same time. But after waiting a few minutes and hitting refresh the library comes back up and you can proceed.

However, there are several instance where the tape library information on the LTC does not match the TLS. For example, the TLS shows one library, two drives, and twenty slots, but the LTC only shows part of that. The easiest solution in this is to start over. However that is not documented anywhere. You could try the below, which won’t work.

AddLibraryServerForDpm.exe -DpmServerWithLibrary TLS.FQDN -remove
SetSharedDpmDatabase.exe -removedatabasesharing

Why doesn’t this work? Because it still leaves the linked server objects in SQL server:

Another point is the sharing related settings in tbl_DLS_GlobalSetting table are not removed either.

GlobalServerDPMDB
LinkedServerName

So here’s the proper way to clean up and start over on the LTC:

1 Run the built-in commands to remove sharing:
AddLibraryServerForDpm.exe -DpmServerWithLibrary TLS.FQDN -remove
SetSharedDpmDatabase.exe -removedatabasesharing

2 Manually removed the linked servers and entries in the tbl_DLS_GlobalSetting, or just run this SQL query (note the redundant ‘USE [master]’ and ‘GO’ could probably be removed, but I haven’t tested the process without them):

USE [master]
GO
EXEC master.dbo.sp_dropserver @server=N’GlobalServerDPMDB’, @droplogins=’droplogins’
GO
USE [master]
GO
EXEC master.dbo.sp_dropserver @server=N’NewGlobalServerDPMDB’, @droplogins=’droplogins’
GO
USE [master]
GO
EXEC master.dbo.sp_dropserver @server=N’OldGlobalServerDPMDB’, @droplogins=’droplogins’
GO
use [DPMDB]
DELETE FROM [DPMDB].[dbo].[tbl_DLS_GlobalSetting]
WHERE PropertyName = ‘GlobalServerDPMDB’ OR PropertyName=’LinkedServerName’
GO

3 Re-enable tape library sharing
4 Open SQL MGMT studio and run the following on a new query:
USE [DPMDB]
select * from tbl_mm_library
GO
5 There should be an entry for robot with all the settings expected. However, the DPM GUI still doesn’t show it. So in the query window results, scroll to the right to the IsOffline column. If it’s set to 1, aka TRUE, then that’s why it’s not showing up.
6 Run the below query replacing the [LibraryID] with the vaule from the results from step 5 in the LibraryID column:
update tbl_MM_Library
set IsOffline = 0
where LibraryId = ‘[LibraryID]’
7 Restart the DPM GUI
8 Do a fast inventory
9 Refresh the tape library info

That should be it and in a few cases might not work, so you’ll have to restart the process at least once.

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