On Tue, 2 Dec 2003, Joost Mulders wrote:
> 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:
> DLT7000 - 35GB - DLTtape IV
Yes, we're using a DLT7000 drive with DLTtape IV.
> 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
> be selecting a lower density for various reasons.
Density is correct.
> 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 ?
That's exactly what I don't grok, either, which is the problem. The
backup is filling up these tapes, but I can't figure out what the heck
it's putting on them. :)
> 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.
Interesting theory. We are indeed using the cbn devices. I'll have to
look into this.
> 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.
This is something I didn't know, and if this is the case, I could
definitely believe this could be the problem.
I think we're currently running only a single stream, for historical
reasons. However, those reasons don't exist anymore, so I may up the
number of streams, since that'll get more data to the tapes (we have a
library with four drives, two drives per SCSI bus). That may help if this
is indeed the problem.
Thanks very much.
Adam Levin, Senior Unix Systems Administrator | http://www.audible.com/
Wayne, NJ, 07470 "?" he said.