I want to compress backup files to tape using compress on our AIX 4.2

- Our TAR does not have compression.
- I do not want to use local storage to compress as most of the filesystems are pretty full.
- the only compressing tool we have is 'compress'
- tapes are 5Gb 8mm


I am trying this :

change tape block_size=512 (default dd obs value)
tar -cvpdlBf - a_folder | compress | dd of=/dev/rmt0

but it is giving me :
dd: 0511--53 The write failed.
: A system call received a parameter that is not valid.


but using something like this works:
tar -cvpdlBf - a_folder | compress | dd of=/tmp/zzz.Z

Any idea on what is the problem ?

First off, (depending on the type of your tape drive) you have a pretty good chance of not needing any compress at all because most of the IBM tape drives have a hardware compression built in. If you send a compressed stream down to the tape drive it will be compressed a second time which will usually make the file a little bigger (because of the second compression overhead adding), not smaller.

Second, even if it is justified to use "compress" in your case, you probably have to add "if=-" to the "dd" command. AFAIK "dd" doesn't use stdin per default for incoming data. It also might be necessary to state the blocksize. Use "bs=<some number>" in this case to state the block size in bytes.

A third reason might be that you have to adress the tape drive with another device number, maybe "/dev/rmt0.1". Have a look in the manual for the meaning of the minor device numbers with tape drives.

I do not recognize your first statement "change tape block_size=512", usually this is accomplished using the "tctl" command, alternatively use the "chdev" command on "/dev/rmtn".

I hope this helps.

bakunin

I know the client's tape drive are using built in compression. But the problem is that is taking toooo looonnnggggg. Backing up a 10Gb folder's content takes 5 hours. The procedures we use to do the backups (10 database backups between averaging 8Gb spreaded amongst 5 servers with each only one tape drive) have us verify the tapes after we have done the TAR backups. Do do all of this takes 18 hours ! I want to reduce this time as much as possible with 2 ways where one way is using compression before putting on tapes. Using local compression on disk takes 2 hours per DB backups. That is why I was trying to compress to tape using piping.

I'll check the if=- and bs= options.

As for the "/dev/rmt0.1", its probably it. I have seen this in other backups types we do.

The blocksize change command was just a summary of what I did before doing the DD. It is actualy a chdev.

sometimes the backup problem may be coz of the device driver. If proper device driver is not installed then it might cause the problem I have faced it many times.
please check Driver and firmware that might help.

I have no ideas on how to do that. I am only a very basic operator. Our system admin is not a real system admin (lack of knowledge and lack of practic).

This client's system is old and over 20 years old (AIX 4.2).