Hello,
Jesse Keating wrote:
I'm looking for some help determining if my hardware tape library is
doing compression. The documentation for the library says "Compression
is enabled by default unless the backup software disables it" and
nothing really more.
I'm using an Overland Powerloader under CentOS4. I do not have software
compression enabled and I'm trying to make sure that hardware
compression is enabled.
I see different approaches:
- I don't know the Powerloader, but perhaps it has a status display or
status monitoring tool that can tell you.
- You can use 'mt status' or tapeinfo to print the settings of the tape
drives:
# tapeinfo -f /dev/sg4
Product Type: Tape Drive
Vendor ID: 'HP '
Product ID: 'C1553A '
Revision: '9503'
Attached Changer: No
MinBlock:1
MaxBlock:16777215
SCSI ID: 5
SCSI LUN: 0
Ready: yes
BufferedMode: yes
Medium Type: Not Loaded
Density Code: 0x24
BlockSize: 0
Interesting stuff begins here...
DataCompEnabled: yes
DataCompCapable: yes
DataDeCompEnabled: yes
CompType: 0x20
DeCompType: 0x0
... and goes to here.
BOP: yes
Block Position: 0
Or you can try it:
use dd to write as much data as possible to a tape. Use a clean tape not
yet used by any backup software or you will lose data. Make sure the
data you write is compressible - for example, make a shell script that
produces lots of ascii output with some differences. Do not use
/dev/zero or one small file over and over again as that will probably
have your tape drive work in shoe-shining mode :-)
Alternatively, you could observe bacula and see how much data it puts on
a tape. In both cases, when the data you put on a tape is considerably
more than the nominal capacity of a tape it is compressed.
For example, daily backups of a router can fit about 12 GB on a 4 GB
tape here because it saves mostly ascii text logs.
Arno
--
IT-Service Lehmann [EMAIL PROTECTED]
Arno Lehmann http://www.its-lehmann.de
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