[Veritas-bu] too many tapes?

2003-12-02 16:46:27
Subject: [Veritas-bu] too many tapes?
From: Joost Mulders <mail AT j-mulders.demon DOT nl> (Joost Mulders)
Date: Tue, 2 Dec 2003 22:46:27 +0100 (CET)
Hi Adam, 

This is interesting. I looked up the native capacities for all types of DLT. 
Since you say 35GB, I assume you have DLT7000. If not, that may be you problem 
:-) Native capacities are below:

DLT4000 - 20GB - DLTtape IV
DLT7000 - 35GB - DLTtape IV
DLT8000 - 40GB - DLTtape IV

I would say: check you have indeed DLT7000 and you are using IV tapes. If you 
have older (III and IIIxt) you'll get less capacity.

Also: check the density used by the drives. This can be read on the frontpanel 
of the drives if you insert such a tape. It should say "35GB" but the drive can 
be selecting a lower density for various reasons.

What I don's grok is that you say 31GB per tape (sounds reasonable) AND that 
backup already used 80 tapes: 80 x 30 = 2400GB ?

Also: What is the device file used to write to the tape drives? If you use 
compression on the drive (/dev/rmt/Xcbn), it could be that the compression 
algorithm in the drive chokes on "already compressed audio" and actually 
increases the amount of data although I doubt that this would double it.

As a last possibility: These tape drives do their best to keep streaming 
("running"). If you are feeding them not enough data, the drive will start to 
write less tracks on the tape in order to keep running. This will reduce tape 
capacity. If the data rate is falling below a certain (secret I think) limit, 
the drive will do start/stop mode. 

Keep us posted!, 


>I'm trying to do a backup, and it seems to be taking more tapes than I
>expect it should.
>Here are the details:
>NetBackup Data Center 3.4.1
>Solaris 8 master and media servers and clients
>DLT tapes, 35GB capacity
>I'm backing up this client:
>[12:07:49]root AT cdl0 DOT prod:/root$ df -k
>Filesystem           1k-blocks      Used Available Use% Mounted on
>/dev/md/dsk/d0        15334747   3440095  11741305  23% /
>swap                   2269672        16   2269656   0% /var/run
>swap                   2293432     23776   2269656   1% /tmp
>/dev/md/dsk/d10       17413250   2829368  14409750  16% /opt/apache
>/dev/md/dsk/d30      121878754  90953189  29706778  75% /audiblewords/downloads
>/dev/md/dsk/d50      818335041 788567840  21583851  97% /cdl0/bk
>/dev/md/dsk/d60      400461265 330097552  66359101  83% /cdl0/content
>/dev/md/dsk/d20       34820241    239462  34232577   1% /opt/apache/logs
>auspex:/auspex/content 20965708    123653  20632397   1% /auspex/content
>auspex:/auspex/vol02 501558096 375170952 121371563  76% /auspex/vol02
>auspex:/auspex/vol00 501558096 449135476  47407039  90% /auspex/vol00
>auspex:/auspex/tmp   225766096      2592 223505843   0% /auspex/tmp
>auspex:/auspex/vol04 501558096      5324 496537191   0% /auspex/vol04
>auspex:/auspex/vol03 501558096      6696 496535819   0% /auspex/vol03
>auspex:/auspex/vol01 501558096 448260064  48282451  90% /auspex/vol01
>[09:47:06]root AT cdl0 DOT prod:/root$
>I've got the class set up as follows:
>"Active" and "Follow NFS" are checked, all other choices (compression,
>cross mount points, etc) are unchecked.
>The file list to back up is:
>By my calculations, those filesystems total 1,279,211,090k, which is
>1,219 GB / 30 GB per tape = 40.63 tapes. (bpmedialist is reporting I'm
>getting roughly 31GB per tape for those big "volxx" volumes -- it's already
>compressed audio data).
>However, I've used over 80 tapes already, and the backup isn't finished
>yet.  I don't understand why it's taking so many tapes.  These are fresh
>Any ideas?
>Thanks very much,
>Adam Levin, Senior Unix Systems Administrator |
>Audible, Inc.
>Wayne, NJ, 07470            Quis custodiet ipsos custodes? 
>Veritas-bu maillist  -  Veritas-bu AT mailman.eng.auburn DOT edu

Long may you run.

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