LTO5 Tape is not using the complete capacity of 1,5TB (uncompressed) + Compression not working

[konzept]

Hey Guys,

I have a strange problem at one of our customers installation.
I've installed a SAS attached external HP LTO5 drive with 1,5TB/3TB Cartridges. Backup Exec 12.5. It worked well since a half year. As the backup data increased with the time, I have now problems with the capacity of the cartridges, because they are not using the full 1,5TB. 
Backup Exec tells me at 1,26TB already that the tape is full. On some other tape already at 1,06TB.

Is this normal?

Here a screenshot of the tape details after backup:

The second point is the compression: Shure we have a lot of JPEG Files, but also when I exclude all JPEG Files and backup only 3 Windows Servers, the compression is still at 1:1. I did the Compression check with the HP Tape tools and that compressed without problems. Shure this will never be 2:1 but at least 1,1:1 would be a beginnig ;)
We don't use encryption and the Backup Exec Compression option is set to: Hardware compression if available.
Before the backup I've inserted a new cleaning cartridge to be shure that the problem is not caused by a dirty drive.

I hope we can find a way to compress the data, otherwise we must search a second backup location for specific files.

Thanks for your help.

Regards
Simon

[pkh]

It is not just jpeg files which compress badly.  Other files like zipped files, movies, sound clips, etc. also compresses badly.  You got to check your data.  See my article on this subject.

https://www-secure.symantec.com/connect/articles/compression-short-explanation

[konzept]

Thanks for your fast response.

You've written a great explanation of the compression Myth.

So would it in my case be better to turn of the compression off to get more capacity on the tape?

[CraigV]

It's worth a shot...the other option, if at all possible, is to put in an exclusion and leave off the image files...

[konzept]

in my case leaving all jpegs is no option...
let's see this night what happens without compression. I'll post the results.

Once again, thank you for your fast responses.

[konzept]

Bad news. This night with compression disabled it went worse. Effective data on tape 988,71GB. 
Can someone explain these results? 

[Ken_Putnam]

Sounds like  a known issue with v11d and LTO drives reported way back when

(You will lose anything currently on the tapes when doing this, but it should start compressing after doing so)

Use the Quantum utility to re-initialize the tape rather than labeling in BackupExec.  This was never posted as an "official solution", but we never saw any responses from anyone who tried it that it did not work

[teiva-boy]

yup, sometimes you need to do a long erase of a tape, or use the vendor tape drive tools to erase a tape, and try again.  

Outside of that, the latest drivers and firmware for the drives and library are a good thought too.

[pkh]

This means that you are getting compression but not so much as to affect the compression ratio.  You can try software compression and see how much data you can get on the tape.  Software and hardware compression is normally quite close.  If software compression shows almost the same result as hardware, then there is nothing much that you can do to improve the situation.  It means that your mix of data is not compressible.

[konzept]

I've done yesterday a full erase  of the tape with HP Tape Tools.
The backup now completed and wrote 1,262 TB to the tape (value from job list). 1,15TB data is written in the tape details.

But why is he using 1,4TB on the tape with 1,15TB data? It cannot be a "negative compression" problem, because without compression its the same (as seen above).

I've watched now other installations of our clients and ther the data value is always higher than the used capacity on the tape.

Can someone explain me why this is happening?

[CraigV]

You'll always have a bit of overhead with tape, so you won't get a full 1.6TB or whatever the compressed capacity is.

If you're not spanning tapes during a backup, then this would be an acceptable tape utilisation.

What it's saying there is that it read 1.2TB of data and wrote 1.15...so it looks good.

[konzept]

well... 300GB of overhead is a bit to much for 1,5TB of max. capacity imho.

What do you mean with "spanning during backup" ?
I've set the option, to span the tape before backup. Do you man that?

[CraigV]

...if 1 tape is full, it spans onto a second tape...

[pkh]

The "negative compression" is because you are compressing data which is already compressed.  This is explained in my article

https://www-secure.symantec.com/connect/articles/compression-short-explanation

[konzept]

I've already tried (see "bad news" post before) to disable the compression.
Still the same result.
 

[pkh]

As I said before, this means that your data cannot be compressed further.  There is nothing much that you can do about this, short of not backing up the data. 

[konzept · Accepted solution]

Just wanted to let you know, that I've been able to solve the problem.
I did some additional tests with the HP Tape Tools and with the "HP Drive Assessment Test" came out that the device could not write the full capacity to the tape.

HP sent me a new LTO and now it works like it should.
Compression 1,1:1 - Data on tape 1,0TB.

Nevertheless, thank you for your time.

I hope this post helps someone else in the future.

Regards
Simon