[2093] in linux-scsi channel archive
Re: DAT drive density
daemon@ATHENA.MIT.EDU (Pete Popov)
Tue Jul 1 11:17:01 1997
To: Clem Pryke <pryke@aupc1.uchicago.edu>
cc: linux-scsi@vger.rutgers.edu, Pete_Popov@asd.sel.sony.com
In-reply-to: Your message of "Mon, 30 Jun 1997 19:20:09 CDT."
<199707010020.TAA04006@aupc1.uchicago.edu>
Date: Tue, 01 Jul 1997 08:11:14 -0700
From: Pete Popov <pete@jones.asd.sel.sony.com>
Clem,
>I am running RH Linux 4.1 on a Dell Optiplex GX Pro with AHA2940 SCSI
>contoller connected to a Seagate CDT8000R-S DAT drive.
>I can write tapes using "tar cf /dev/nst0 datafile" etc, and read them
>back fine. However the tapes get full after approx 1 GB. It a DDS-2 (4
>GB native) drive so this is not right.
>With a tape inserted "mt status" gives:
>SCSI 2 tape drive:
>File number=0, block number=0, partition=0.
>Tape block size 512 bytes. Density code 0x13 (DDS (61000 bpi)).
>Soft error count since last status=0
>General status bits on (41010000):
>so everything looks good until I write to the tape. Afterwards "mt
>status" reports "Density code 0x13" and I am still getting 1 GB tape
>capacity.
In general, modifying the density code on DAT drives will not do
anything ... unless the drive allows compression to be turned off
by selecting _some_ density, which most drives don't do. If the
drive has a DDS2 tape in it, it will write it in DDS2 mode.
You do have a 120m tape in it, not a 60m or a 90m tape, correct?
>The drive is OK. I can write 4 GB tapes in WinNT. Please help.
Are you backing up the same file on the same tape? If not, that's
the first thing you should try.
DAT drives can waste capacity if the RAW (Read-After-Write) rate is
high. However, if you backup the same file on the same tape under NT,
and you are still getting 4GB, then it's abviously not the RAW rate.
An other possibility is that your drive is repositioning excessively
under Linux due to the small default tar transfer size. If the
drive does not handle repositioning well, it WILL waste some
capacity.
Try a larger transfer size: tar -cb 120 -f datafile /dev/nst0.
A count of 120 is equal to 64KB transfers.
Good luck.
Pete Popov
Sony Electronics
