Backup with tar

[Ezra V. Isacco Di Biase]

Hi all,

I backup my data on a DLT Tape IV (40/70 Gb)
I use the command:

tar cvE file.tgz

the file's size is over 32Gb. After 30Gb of writing the tar command requests another tape to write on! How is it possible?
Is it a problem of density?
Do I have to use different options?

Thanks in advance.
Ezra

[Ralf Puchner]

what version of unix?

without specifying a tape device it will use the environment variable (if exists) or the standard device.

Have a look to the man page of "tz" or "tape" (depending on version) and decide which device to use for the right compression specified by -f flag of tar.

[Ezra V. Isacco Di Biase]

The version is dgux 4.0f

I thought that without -f it should use /dev/rmt0h
isn't it?

[Ezra V. Isacco Di Biase]

excuse me... i forgot my library is a TZ89.

[Ralf Puchner · Accepted solution]

the library is not used with the tar command and doesn't matter. Have a look into the man page specified (here "man tz" and select the density depending on your tape model e.g. tz89 - it is very simple and explained in detail).

compression will only be used with nrmt0h on tz89 and tape IV. Without compression data will be 30-35 GB.

But be sure the backup data are not compressed (e.g. no pictures, gzip archives etc). Otherwise the limit is still 35GB because already compressed data can not be compressed anymore - but this is quite clear.

[Joris Denayer]

Ezra,

First, You are making a backup of an already compressed file (.tgz). This means that the Tape can't compress it anymore.

Second, the TZ89 can only write Maximum 35GB uncompressed on a Tape IV cartridge.

I don't know exactly how the tape compression algorithms will react on already compressed data. But, I have seen software compression software where the compression of already compressed data resulted in a larger file.

Hope this helps

Joris

[Ezra V. Isacco Di Biase]

I beg your pardon!!!!
:-)

I didn't thought it was already compressed!
Thanks to all to stand me!

Ezra

[Ezra V. Isacco Di Biase]

I'm here again!

Now I've tried to do a backup with this command:

tar cvEf /dev/nrmt0h /my_data_directory

Now, without zipping the files the backup is larger than 60Gb and it asks me for a second tape again!!!
I haven't specified a blocking factor because I have not understood how to use it. Should I?

Thanks... and going crazy!

[Ralf Puchner]

blocking improves speed and depend on the tapedrive and I/O capability.

If 60GB doesn't fit on the tape please check how much data must be saved by using

# du /directory

(directory is the directory you want to backup)

[Ezra V. Isacco Di Biase]

Ralph,

the output of du -k is:

4238691 /storage/dir1
10825118 /storage/dir2
12398735 /storage/dir3
3525016 /storage/dir4
6840450 /storage/dir5
18381615 /storage/dir6
3993611 /storage/dir7

Total: 60,589 Gb

Our tape should be enough! I do not understand.
thanks.

[Ralf Puchner]

The tape stores 35GB uncompressed but 70GB compressed. This is the answer, your data can not be compressed well to fit the tape.

The limit of compressed data is in range between 35 to 70Gb depending on the format.
There is no garantee for 70GB per tape.

If using a real backup software like networker leads to several savestreams which could be better compressed than a simple singlestream tar command.

[Ralf Puchner]

Btw. if tape is not in stream mode (data is not sent as quick as tape will write it) the backup-time increases and blocking is getting worse (due to fillbytes). This is the reason using professional backup software with multiple savestreams.

[Ezra V. Isacco Di Biase]

Thanks Ralf.

I took a long time to understand but now I know how to solve the problem.

You were extremely helpful.