Veritas-bu

[Veritas-bu] Space left on Tape

2006-07-19 02:11:23
Subject: [Veritas-bu] Space left on Tape
From: simon.weaver at astrium.eads.net (WEAVER, Simon)
Date: Wed, 19 Jul 2006 07:11:23 +0100
Hi Bob
Re: the EOM - End Of Media - any ideas why then, that Netbackup is reporting
status 84 for them? Just bit confused why it only seems to be happenign on
the Media Servers and nothing else

Regards

Simon Weaver
3rd Line Technical Support
Windows Domain Administrator 

EADS Astrium Limited, B32AA IM (DCS)
Anchorage Road, Portsmouth, PO3 5PU

Email: Simon.Weaver at Astrium-eads.net



-----Original Message-----
From: bob944 [mailto:bob944 at attglobal.net] 
Sent: 18 July 2006 16:27
To: veritas-bu at mailman.eng.auburn.edu; 'Justin Piszcz'
Cc: 'Dave Markham'
Subject: Re: [Veritas-bu] Space left on Tape


> > Dudes is there any way of saying how much space is left
> > on a particular tape? I have had a look around but am a
> > bit lost.
> 
> Yeah, run bpmedialist and compare with vmquery.

That answer makes no sense.

Dave, a tape holds as much as it holds, period.

In contrast to a disk (has _exactly_ so many cylinders/tracks/sectors and is
usually not compressed); tapes write varying lengths of data, separated by
gaps of different sizes; usually compressing data with variability in the
data, in its fit in the drive buffer, in the firmware algorithm on that
drive; with unpredictable skips over flawed patches of tape; and to tape
length which is not uniform.  The same tape, written in the same drive with
the same source data can vary; the same tape, same drive, backing up
something different will likely be quite different.  Throw in the variables
and and... well, I've seen a range of 4xxGB to 12xxGB on full SDLT600 tapes,
for instance.

An available_media listing with a bunch of full tapes will show you the
variability and give you a rough guide of what to expect from a given pool
and retention (more variability if you use one pool for many/all types of
backups, less if you have pools which handle specific clients and specific,
non-volatile data).

When a tape hits EOM (Simon:  End Of Medium to your question; used to be End
Of Tape by detecting a foil sticker) and NetBackup moves on to another tape,
you have zero space left.  Anything else is an approximation.


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