ADSM-L

Re: 3592 tape read performance

2006-07-31 15:10:45
Subject: Re: 3592 tape read performance
From: Thomas Denier <Thomas.Denier AT JEFFERSONHOSPITAL DOT ORG>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Mon, 31 Jul 2006 15:09:04 -0400
-----"Survoy, Bernard J" <bernard.survoy AT sun DOT com> wrote: -----

>Sounds like you have an issue on some volumes with the VCR (volume
>control region). This structure is used (among other things) to
>support high speed search operations.  If the VCR is invalid or
>damaged, the drive will go into a low speed (essentially sequential
>scan) until you get to the data location you want (takes forever,
>if you look at the drive, it looks like it is reading tape). I know
>on Sun/STK enterprise class drives, we have a similar structure
>called the MIR (media information record); this structure is
>rebuilt during the sequential scan up to the point where you
>successfully locate the data.  A subsequent access beyond this
>point is will rebuild the structure from that point forward.

Just how slow is the linear scan? I am in the process of executing
a 'move data' for a problem volume. The process moved 22 gigabytes
in the first hour or so, and has ostensibly spent almost 5 hours
working on a single 4.7 gigabyte file. How long should I wait for
this one file before I conclude that I have a problem other than
lost VCR information?

What do I do if I decide at some point that the 'move data' is a
lost cause, and want to try 'restore volume' instead? The 'cancel
process' command is cleverly designed to be useless in this sort
of situation; the process will not end until it finishes the current
file. Is there a way to get TSM to stop a data movement process inmid-file?

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