[Veritas-bu] Howto check the approx. available space on a tape?
2007-03-29 11:21:04
Subject: |
[Veritas-bu] Howto check the approx. available space on a tape? |
From: |
ddunham at taos.com (Darren Dunham) |
Date: |
Thu, 29 Mar 2007 07:21:04 -0800 (PST) |
> Martin, Jonathan (Contractor) <JMARTI05 at intersil.com> wrote:
>
> > There's no way to tell exactly how much more data a single tape will
> > hold, since anything better than 100GB (in your example) is compression
> > and compression varies by file type.
>
> Yes, I know. I'm not looking for an exact number. I don't know how
> LTO tapes exactly work, but I suppose that the tape is written now
> until a certain "position". If the tape is 609 meter long, it might be
> written up to 550 meters, which would be about 90%. Or is that assumption
> completely off?
That's not exactly how they work, but it's not why the question is hard
to answer.
The main problem is that there is no standard for asking a drive any of
that information. That's why Netbackup (and every other backup system I
know of) is written so that it doesn't need that information.
I assume that back when a lot of the tape drive standards were being
written that many drives could not detect either the capacity of a
loaded tape or their current position along it.
I do suppose that modern drives keep track of it but don't make that
information available in any standard way. At least the AIT Mammoth
drives had a utility that would query the drive to display tape usage
and compression average to that point. I would guess that such
information is available for LTO as well, but I don't know how to ask
the drive for that information.
--
Darren Dunham ddunham at taos.com
Senior Technical Consultant TAOS http://www.taos.com/
Got some Dr Pepper? San Francisco, CA bay area
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