How to maximize compression on DAT24/HP-UX

[John Downs_1]

Hi, I have a surestore DAT24eu attached to HPC240+ running HP-UX 11.00. The spec states that is can store up to 24gig but I am failing at about 10gig. My device file is: c1t3d0bestn
Am I getting the maximium compression? How do
I get better compression? I'm using dump.

Thanks
-john

[Robert_Jewell]

First off what type of tapes are you using? Your tape drive is of a DDS-3 format. If you are using DDS2 tapes you wont get all the compression the drive is "rated" for. Also the lenght of the tape will obviously determine how much can be stored.

If all that is fine above, then you may want to check the DIP switches on the bottom of the tape drive. Defaults for DDS3 are switch 3 = off, all others on.

-Bob

[John Downs_1]

Hi, the tape is a DSS4 and the length is
120 units. I was wondering/hoping someone
my have the optimum configuration for maximizing the amount of data to put on the tape. I'm using dump with the following options: 0udsf 60000 4000 $tape
I don't know if 60000 and 40000 are the best values for tape density and length. Do you?

Thanks

-john

[Vincent Farrugia]

Hello,

From "man dd":

'WARNINGS

You may experience rouble writing directly to or reading directly from a cartridge tape. For best results, use tcio(1) as an input or output filter. For example, use

... |dd ... |tcio -ovVS 256 /dev/rct/c4t1d0

for output to a cartridge tape, or

tcio -ivS 256 /dev/rct/c4t1d0 |dd ... | ...

for input from a tape cartridge.'

HTH,
Vince

[Michael Tully]

Hi,

DDS tape are rated as such

DDS 90M 2.6Gb native
DDS2 120M 4 Gb native
DDS3 125M 8 Gb native
DDS4 150M 12 Gb native

dd is not a real good backup tool
in relation to getting good compression.
There are others that are far more
efficient and compression with always
depend on how well the data can
be "squeezed". So if you have 12 Gb
tape as above the worst case should be
you will 12Gb onto a tape no matter what
tool is used.

-Michael

[John Downs_1]

Thanks I'm all set now!

-john