SUMMARY: DLT4500 and changer on 4.0B

From: Joern Wilms <wilms_at_astro.uni-tuebingen.de>
Date: Thu, 14 May 1998 08:31:04 +0200 (MET DST)

Hi,

I few days back I asked the following question

>
> Dear Managers,
>
> we've recently switched our main backup machine from VMS to Unix
> (V4.0B). Our backup medium is a Quantum DLT4500 with a media changer
> unit. Both devices have been entered into the /etc/ddr.dbase (see
> below). Due to financial reasons (my employer being an university, after
> all...) I'm forced to do the backups with tar. The current strategy is to
> tar each filesystem individually onto the DLT, with each filesystem
> having a size of about 10GB (although we've also a 65GB RAID, but that's
> another story...). My problem is that the DLT does not appear to switch to
> the next tape when the EOM is reached.
>
> Therefore:
>
> 1. How do I configure the DLT/Changer such that it switches automatically
> between the tapes in a tapeset?
>
> and/or
>
> 2. I could switch manually between tapes, but how do I do that
> softwarewise so that I can run my backups overnite?
>
> Thanks for your help,
>
> Joern Wilms
> wilms_at_astro.uni-tuebingen.de
>

and soon got very good and helpful replys from

Jim Belonis <belonis_at_dirac.phys.washington.edu>
Susan Rodriguez <SUSROD_at_HBSI.COM>
Alan Rollow <alan_at_nabeth.cxo.dec.com>
Mitch Bertone <mbertone_at_gtech.com>

Below I summarize their answers:

1. with

   mt rewoffl

   the tape is not only rewound, but also ejected and the next tape is put
   into the drive. Indeed, it works! (although I don't know yet what
   happens when the last tape is ejected -- hadn't the stamina to wait and
   check that...)

   Several people recommended using expect
   together with tar to automatically catch tar's requests for
   a tape change by running the above command (plus a sleep). This way the
   production of tar savesets larger than one tape is possible. Others
   recommended to just make sure that individual tar's don't fill up the
   tape and then issue the mt-command between the tar-commands. I'll
   probably adapt the latter approach in the future except for the backup
   of our 65GB RAID.

2. Apart from informing me about `mt rewoffl' several of the answers I got
   contained comments about the choice of backup-tool used (tar in my
   case). Some people strongly recommended (v)dump instead of tar, and one
   pointed me to a quite interesting paper on different backup strategies
   (http://www.phys.washington.edu/~belonis/backup-torture.ps [although
   this paper is from 1991, most of the information might still be valid --
   except for gnu-tar...]). vdump also appears to be able to handle
   multi-tape backups including sending the appropriate commands to the
   media changer.

3. Some people recommended commercial or public domain software to do
   backups and/or switch the tape. I haven't looked into these yet. Most of
   the commercial products unfortunately appear to be too expensive for use in
   a university environment. Here are the products mentioned (in no
   particular order)

       seltape (tape changer, available for SGI Irix).
       Boston Business Computers VMS Backup emulator for Digital Unix.
       Trovli
       CA Unicenter.

Thanks again to all who answered, this list has again proven to be VERY
useful!

Cheers,

Joern
Received on Thu May 14 1998 - 08:32:07 NZST

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