From: Spurgeon, John P (john.p.spurgeon@intel.com)
Date: Mon Apr 08 2002 - 16:53:33 EDT
I'm developing a new OS build that will be installed on hardware that has
already been deployed. I am trying to back up the operating system (system
drive 0) to a 120 meter DDS-2 tape. After switching to administrative mode
(init 1), I'm using the dd command to perform the backup. For example:
dd if=/dev/rdsk/c1t0d0s2 of=/dev/rmt/0u bs=32k
My problem is that I keep getting "short write" errors after the dd command
has run for a little over 2 hours. For example:
dd: unexpected short write, wrote 0 bytes, expected 32768
264555+0 records in
264555+0 records out
The problem is repeatable and has occurred on multiple systems with the same
OS build. The tape drive is an HP SureStore DAT 8. I've tried DDS2 tapes
from two different vendors (HP and Imation) with the same result. System
drive 0 consists of two 8.683 GB Seagate Cheeta ST39103LC hard drives in a
RAID 1 hardware mirror. The format command says that partition 2 (the backup
partition) is approximately 8.45 GB.
What's frustrating is that this back up process used to work with our
previous OS build. I know that we're really pushing the limits of the DDS2
tape. Generally, people say that a 120 meter DDS2 tapes hold 8GB of
compressed data; however, I've seen one report that says the amount of data
the tape can store varies anywhere from 7-12 GB
(http://www.linuxdoc.org/HOWTO/Unix-Hardware-Buyer-HOWTO/backups.html). I'm
wondering if we just got lucky with our pervious build and now we're not
able to fit all the data on the tape due to variations in the amount of data
on the disk or the degree to which the data compresses.
I haven't tried using a different tape device yet (e.g. 0c), but I'm not
very optimistic about that approach. In the worst case, I suppose I could
just make the drive look smaller via the RAID configuration utility. Any
other suggestions?
Thanks,
John Spurgeon
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