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Enabling Compaction on Ultrium 4-SCSI tapedrive.

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The Brit
Honored Contributor

Enabling Compaction on Ultrium 4-SCSI tapedrive.

HP Support is suggesting that I enable compaction on one of my tapedrives to try to address some serious degradation that I am trying to troubleshoot.

Although I dont see the logic in this suggestion since the other drive (i.e. the one that is working fine), also has compaction disabled, I am prepared to try it out. I have found the option in LTT to allow compaction to be enabled, however the device (at the VMS level) still says "compaction disabled"

Question is, Is there anything else I need to do at the VMS level to enable the tape drive for compaction, "IO AUTO", "IO SCSI_PATH_VERIFY",...???

thanks \

Dave.
10 REPLIES
labadie_1
Honored Contributor
Solution

Re: Enabling Compaction on Ultrium 4-SCSI tapedrive.

May be use dcl commands, such as

init/media=compaction ...
mount/media=compaction ...
backup/media=compaction ...

abrsvc
Respected Contributor

Re: Enabling Compaction on Ultrium 4-SCSI tapedrive.

I don't believe that the device will show compaction enabled unless it is in use. A SHO DEV of the device should show that the controller "supports compaction".

Using the commands in the previous reply should enable compaction for the task/job and be reflected in the SHO DEV while in use.

Dan
The Brit
Honored Contributor

Re: Enabling Compaction on Ultrium 4-SCSI tapedrive.

Thanks to both of you. Both correct.

Follow up question. If these qualifiers only need "controller supports compaction" to work, is it actually necessary to go through LTT to enable compaction.

I assume that when I use LTT, I am enabling some kind of hardware compression.

???

Dave
P Muralidhar Kini
Honored Contributor

Re: Enabling Compaction on Ultrium 4-SCSI tapedrive.

Hi Dave,

Check the following link -
* What do Throughput, Capacity and Compression have in common?
http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=1062137

This talks about tape compression using LTT.

Hope this helps.

Regards,
Murali
Let There Be Rock - AC/DC
Ian Miller.
Honored Contributor

Re: Enabling Compaction on Ultrium 4-SCSI tapedrive.

and
SET MAGTAPE/MEDIA_FORMAT=COMP
too
____________________
Purely Personal Opinion
Bob Blunt
Respected Contributor

Re: Enabling Compaction on Ultrium 4-SCSI tapedrive.

Dave, using LTT to set/enable compaction implies that the drive has a mode page entry that can be changed to do so. In some cases you'll also find that a drive might have a physical switch setting that enables or disables compaction. Its impossible to know that without knowing the exact tape drive model and having access to, at least, it's installation guide.

In any case it can't hurt to try, can it? I would expect for the drives to "display" different characteristics from LTT's diagnostics if one was setup incorrectly. There shouldn't be any changes required in the way VMS detects the tape drive and the unit's capabilities should be detected from it's SCSI mode pages... Just out of curiosity, though, I think I gathered that your Ultriums are connected through the SAN (drives have been referred to as MG devices?) and are they installed in a loader/library? Are they directly connected to the SAN or to a MDR or NSR (or an encrypting device like a DECRU)? I've seen some really obscure problems in those configurations.

bob
The Brit
Honored Contributor

Re: Enabling Compaction on Ultrium 4-SCSI tapedrive.

Hi Bob,

The tapedrive in question is an Ultrium 4-SCSI 1840 FC drive. One of two which are installed in an MSL4048 (Part# AJ038A)

One drive in the library (MGA4) is funtioning fine, however the other drive (MGA5) is performing miserably.

I attempted to enable compression through LTT, however I am not convinced that I succeeded because the next time I ran a support ticket, it still said that compression was disabled.

I did try running some tests using the VMS qualifiers "/Media=Compression". Surprisingly (to me), this appeared to work OK. (although I am not comfortable "Having to" use them)

I then went back into LTT and explicitly disabled compression on the drive.

and I am now running some tests to see where I stand.

Dave.

Bob Blunt
Respected Contributor

Re: Enabling Compaction on Ultrium 4-SCSI tapedrive.

Dave, "...one of two of which is installed in a MSL..."? Just checking to see if I read that correctly. So one lives in a library and one is a...standalone "desktop" unit or are both in the library? I know that most library style loaders usually have a form of "jukebox" control that can be configured either directly connected to the SCSI/SAN or daisy-chained with the other drives if connections are limited. I may need to research further because my exposure to SAN-based library systems is limited. Mainly to SCSI-based units that require either direct connection to SCSI or to the SAN through a MDR or NSR.

In any case the library itself shouldn't be causing any limitation since most of the drive connections don't have to go through much logic from the external panel interface to the connections on the drive itself.

bob
The Brit
Honored Contributor

Re: Enabling Compaction on Ultrium 4-SCSI tapedrive.

Both in the MSL. That was what was making this problem so frustrating.

San connection was directly to the FC port on the back of each drive.

Both drives use exactly the same infrastructure.

The only single point of divergence is the actual fiber running from the SAN Switch port to the back of the drive (obviously both drives connect to separate ports.)

distinct performance differences (see attachment.)

HP sent a replacement drive, which I installed and tested this morning.

Problem resolved.

Thanks to all for your help

Dave.

The Brit
Honored Contributor

Re: Enabling Compaction on Ultrium 4-SCSI tapedrive.

This question was an offshoot of a LTo4 tape drive performance problem. The problem drive has been replace, so issue is resolved.

thanks

Dave