How many LTO 3 tapes should Networker require to backup approx 2.2TB?

[Crono]

Hi all,

I'm having an issue with Networker 7.3.2 and I cannot find the cause of the problem. We are backing up approxiamtely 2.2 TB of data over the course of the weekend. We have Networker running an ADIC iScalar tape library which has 2 LTO-3 tape drives. There are 8 tapes in there reserved for this job which I think is more than enough for this task. The job easily blew through all 8 tapes and is now asking for a 9th! For tapes with at least 400GB capacity this is just wrong.

Can anyone give me some guidance on where to look for the cause of this problem?

Thanks in advance!

-C

 

[605]

Most likely your tapes have been filled prematurely. NW assigns the status full, if he can not recover from a hard write error. The cause of course can be anything.

 

[Calippo]

Errmmmm

3 or 4, normally but i guess it depends on the compression effeciency.

regards

 

[Crono]

Thanks for the responses it's much appreciated.

A couple of the tapes did not have any info on them. The drive had a problem reading the tapes and marked them as full. So that solved at least part of the problem I am having.

I decided to redo a particular part of the backup job which amounts to about 1TB in size. The job ended up taking 2.5 LTO3 tapes which I still found wrong.

I brought this up with my boss who pointed out that the files that I was backing up were already compressed on the fileserver to beign with. So it is acutally 1Tb compressed.

I guess my question is is the fact that the files are already compressed what is causing the backup to span som many tapes?

Thanks in advance!

-C

 

[605]

You should never compress the data on the source (client) AND on the tape drive. Besides the fact that client site compression uses additional resources, the data could in fact increase in size.

Unfortunately, it is not easy to switch off tape compression, especially not on Windows where no other device name exists.

Of course the factor depends on a lot of different issues - i guess nobody except someone who uses a similar environment can explain the effect and the factor precisely.

My suggestion:
Try to run a backup without the tape drive compression. And if you want to reuse the old tapes, be careful when you relabel them. As each backup software must read the tape label first to detect a valid label, the tape drive's firmware will switch to the found density instead of the one you manually selected. It is better to erase a tape first using a routine like NetWorker's tapeexer(cise).

 

[Calippo]

If you want to know what data is on the tapes I suggest you run an mminfo report on the tapes in question. Dont forget to include sumsize, totalsize,ssid,ssflags,clflags.
You may find that you have aborted savesets munching up space on your tapes.

Complession is normally set on the tape drive using pins and the default would be on. In either case, if the data is compress before it shoots up the cable then the tape drive is hardly likely to compress it further.

regards

 

[Chapter11]

1TB compressed should be 2.5 LTO3s. The capacity of an LTO3 is 400G compressed, so things look completely normal.