SUMMARY: DLT 7000 expected capacity

From: David Robson (
Date: Wed Jul 30 1997 - 10:09:02 CDT

Thanks to all those who replied. I guess I got the answer I expected but
not the one I wanted. ( I'd hoped someone had got 70GB out of a DLT) :-(

As I mentioned, with our SUN DAT drive, we get an _average_ of 4GB per DAT.
If I take the maximum capacity of the DAT to be 5GB, and given that the
nature of the data hasn't changed, then I should expect an _average_ of say
56GB from the DLT.
The DAT has been known to reach and even exceed expected capacity! So where
is my missing 7 - 21GB on the DLT!

I guess the answer will be somewhere in the differance between the helical
scan and the linear technology..... At least its damn fast and has more
capacity than my ol' 20GB DAT stacker. (And more reliable) 8-)
The replies I received mostly underlined that the compression of 2:1
depended on the type of data being recorded, I was aware of that, and as I
have mentioned, I was comparing to the capacity achieved with DAT.

Someone mentioned that the device I was using may not be correct. It was
suggested that I use /dev/rmt/0cbn rather than /dev/rmt/0ubn. The DLT
manual only mentions /dev/rmt/0ubn for "70GB". The man page for mtio refers
to them as equivilent devices.

Only one person had heard about strange streaming (not steaming as I miss
typed):) behavier of the DLT, but without a fix unfortunatly...

One point that was highlighted by this is that you should base your
selection of a backup device on the "native capacity" of the drive. I have
another 24GB of disk comming soon and I won't have a hope in hell of
backing up all our disk on one tape. (Lucky I still have the DAT!) Besides,
I only just got the money for the single DLT, a stacker would have been out
of the question!

Thanks to:
"Feltner, Rodney" <> (Marc S. Gibian)
"David Sinn" <>
Jason Marshall <> (Robert D. Worsham)
John DiMarco <>
James Ashton <>
From: "Rick von Richter" <>
Bob Woodward <>

My original post:

Hi guys, I believe this may be old ground but I couldn't find much in the FAQ!

We have a SUN DLT 7000 with a documented (SUN) capacity of 70GB, assuming 2:1
compression. The best I can get is 49GB using Networker 4.2.6 on an Ultra 2200
running Solaris 2.5.1

I have the st.conf as described in the manual, and I am using /dev/rmt/0ubn.

We were previously using DAT and getting an average of 4 GB on 90M tapes.

Am I doing something wrong? Or is 50GB all I should reasonably expect?

PS The front panel indicates that I am using 35GB mode compressed. Should I
use the option to set it perminatly to this mode in hardware? I have heard
that the DLT will drop out of compression mode to aid steaming if the
incomming I/O is to slow...

David Robson
Davtin Systech Pty Ltd

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