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SCSI tape drive cluster troubleshooting assistance

Posted on 2016-08-31
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Last Modified: 2016-09-20
4 tape drives:  Fileserver, Exchange, Tandberg, LTO2 (don't ask about the names...)
Using Symantec Backup Exec 15 version 14.2 (I know we're behind, discussing a new solution in 2017)
"Inventoried" all 4 tape drives
Attempted to backup "Intranet"(smallest backup job we have, ~250MB) to "Exchange" -- failed with physical device error
Removed all tape drives EXCEPT fileserver.  Plugged directly into Fileserver tape drive with terminator, succeeded.
Plugged into Exchange, succeeded.
Plugged into Tandberg, succeeded.
Plugged into LTO2, succeeded.
Connected FileServer + Exchange - Succeeded
Connected FileServer + Exchange + Tandberg - succeeded
Connected all 4 - failed
Connected FileServer + Exchange + Tandberg = succeeded
Cluster is in order as follows:  1. Fileserver 2. Exchange 3. Tandberg 4. LTO2

Why would I back up just fine to LTO2 while directly connected, but once I add it to the chain/cluster, my job fails.  On the individual tape drive tests I was plugged directly into that tape drive and the backup job was pointed at each tape drive I was plugged into.  Once I added more than 1 tape drive I was backing it up to "Exchange" as that's the designated destination for the backup.  As I state, with 2 tape drives it works, with 3, it works, add the 4th and it fails.
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Question by:Daniel Checksum
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LVL 38

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by:Adam Brown
Adam Brown earned 250 total points
ID: 41778835
Check your SCSI Device IDs on each of the tape drives. If you're failing with all of them plugged in, it's most likely that two of the drives are set to use the same SCSI ID number. Each SCSI ID can only exist once on any chain, so if two devices have the same ID number set, they'll fail.
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by:Daniel Checksum
ID: 41778909
Where/how would I find the SCSI ID?  I've googled how to do it on 2008 R2 for a bit and I can't seem to find a solid answer.  In Backup Exec they show up as HP0001, HP0002, HP0003, and Tandberg
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by:Adam Brown
Adam Brown earned 250 total points
ID: 41779177
SCSI IDs are configured on the hardware. There's usually a switch, button, jumpers, or some other method that defines the hardware ID for the device. It depends on the model of the drives. If they are internal drives, there are usually a set of jumpers between the SCSI connector and the power connector.
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LVL 16

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by:Gerald Connolly
Gerald Connolly earned 250 total points
ID: 41779361
You actually have 4 servers connected to 4 tape drives via a shared SCSI bus?
So that's 8 SCSI id's required.

Has this ever worked? If so what happened when it suddenly stopped working? What was changed.

A diagram of how your cluster is wired (for disk and tape) would help!
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Author Comment

by:Daniel Checksum
ID: 41779847
There are 4 SCSI tape drives connected to ONE server.  That ONE server runs backup exec and connects to other servers to back up data via the remote agent.  Cluster is wired as I stated in the question.  First FileServer, then "Exchange, then Tandberg, then LTO2.  LTO2 has/had a terminator on the SCSI out.  Currently LTO2 is removed and I am terminating at Tandberg as LTO2 was causing an issue.  Still working out the specifics as some backups run and others don't to different tapes.
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by:Daniel Checksum
ID: 41780107
Update,  I think we've narrowed down the problem to a failing/aging LTO4 drive.  the "Fileserver" drive barely wrote 1.5MB in 20 minutes.  I moved the same tape to the "Exchange" drive and it ran 19GB in 20 minutes.  Gonna let it run so I have a good backup but then I'm going to take out the "Fileserver" drive and see if all my jobs can complete(besides that one)
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by:Gerald Connolly
Gerald Connolly earned 250 total points
ID: 41780936
Wow, so you have 4 x LTO4's on one SCSI bus!
19GB in 20mins is slow very slow!!
That's just under 1GB per minute, a LTO4 is capable of over 7GB per minute.

The drives are probably shoe-shining a lot, at that speed  - 1GB/min = 15MB/sec (approx) way below the minimum speed for a LTO4 to stream (min is 33-40MB/s depending on the model). That's a great way to wear out tapes and drives

I hate to think how slow things are when more than one drive is being used simultaneously
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LVL 16

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by:Gerald Connolly
Gerald Connolly earned 250 total points
ID: 41780938
A SCSI bus per drive would help, but only if your server is capable of driving 4 tapes simultaneously above the min speed
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by:Daniel Checksum
ID: 41781584
I'll provide my supervisor with this advice, he may want to move to that set up.  I'm assuming you mean to get a SCSI card with 4 ports as opposed to the 1 and connect each to their own port?  Instead of "clustering" or "chaining" the drives?  That would make a lot more sense to me personally but this is the first company large enough for me to deal with tapes.  Been 100% disk/cloud backups elsewhere.  I'm sure that wouldn't be more than a few hundred dollars to implement too.  HP Proliant G7 (can't remember exact model) can fit a 4-port external SCSI card?
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LVL 38

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by:Adam Brown
Adam Brown earned 250 total points
ID: 41781648
Honestly, with the capabilities most modern backup solutions have, and the ever lowering cost of high availability solutions, tape drives make almost no sense even for large companies with a lot of data. They may cost less for hardware, but the expense of managing the things , keeping track of and securely storing tapes , and the continuing costs of replacing old tapes very rapidly overwhelms any early cost advantage they have. That doesn't even include the additional costs associated with trying to restore from tapes, especially when you end up with a tape that has gone bad prematurely. At the biggest company I contracted with that used tapes, taking care of the things was literally half my work week, and that was after a year of constant process development and improvement. Prior to the company I worked for being contracted to work for them, they had two full time employees managing just backups, tape logistics, and recoveries.

Anyway, sorry for the rant, but I seriously don't think tape backups make any kind of sense in modern IT.
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Gerald Connolly earned 250 total points
ID: 41782509
@Daniel - Actually i think 4 x 1-Port would be better, you need to look at the number of PCI-E slots you have available.

Then there is the throughput of the HBA and the SCSI bus and then the fact that the Drive has a minimum speed of something over 33MB/s to stream.

Biggest problem is usually getting the data to the tape drive quick enough (ie off disk).

@Adam - Its Horses for Courses, Tapes dont make sense in some environments and disk based/cloud backups dont make sense in others

Environments that only use a few tapes per day (as in this case) and already have a tape-based infrastructure in place, it could be quite expensive and very disruptive to move to a disk/cloud system. That said, if their data volumes are small then it might make sense especially if they have good internet connections, to use the cloud instead.
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Author Comment

by:Daniel Checksum
ID: 41787791
OK, wasn't the tape drive.  I did a LOT of troubleshooting yesterday, moving cables, moving terminator, etc.  I think we've narrowed it down to a limitation on the SCSI card and/or the terminator.  Ordered an additional card and additional terminators and cables.  Will update when I have those in hand.  

We ARE looking to move off the tape backups but we're still dependent on them for the time being.  When the budget frees up a little bit we've got some "big" plans for offsite backups.
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LVL 1

Author Closing Comment

by:Daniel Checksum
ID: 41807779
Back-pedaled a bunch, using older hardware with newer software resolved it.  I have no idea what actually was the problem.  We're looking into a different solution now.
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