Backup Randomly Exceeds Tape Size?

[IanW82]

Hi, 

Windows 2008 R2 Server, Backup Exec 2014, LTO-3 Tapes / Drive

I am exeperiencing a strange issue, we backup up pretty much identical data on a daily basis, lets's say for arguments sake, 5GB is the absolute most the backup size will fluctuate. 

One day the backup will successfully complete and write the data to tape with a total size of 542GB. The next day I will come in and the backup is stopped waiting for a second tape yet is has only written 535GB? 

All tapes are the same HP LTO-3's, backup is set to always overwrite and I have even tried new tapes and run in to the same issue?

Any ideas? I am at a loss :\

Thanks! 

[pkh · Accepted solution]

It depends on the type of data. If somebody happens to save a zipped file or a picture, you can get more data after compression than what you have started with. See my article below. https://www-secure.symantec.com/connect/articles/compression-short-explanation It would be easier to just cater for two tapes or get a higher capacity tape drive and tapes

[CraigV]

...you need to check those tapes to see if compression works on them or not. For this you'd need the tape manufacturer's diagnostic utility and a tape you can overwrite. This will do a compression test on the tape to see what you're getting. It might be a case of LTO3 tapes being old now and not having the same functionality as new.

pkh's suggestion is a good one...LTO5 should be well priced now, depending on your country.

Thanks!

[IanW82]

Thanks for the replies, we are in the process of spec'ing the upgrade to LTO-5 but for the time being I would like to get it working. 

I did try to download the HP Diagnostic utility but the HP website is succeeding in getting worse everytime I try to use it, I can find the info page about the software but it seems impossible to download, just sends you around in circles - rant over! 

[CraigV]

Try this link Ian (don't forget that HP have split so this makes things very confusing!):

http://h20566.www2.hpe.com/hpsc/swd/public/detail?sp4ts.oid=406731&swItemId=co_149019_1&swEnvOid=402...

Thanks!

[Larry_Fine]

two guesses:

1) your daily data is just barely going over or under a 1 tape thresh-hold as Cragi & pkh have mentioned.  You might investigate software compression instead of hardware compression as apossible workaround, YMMV.

2) you might have old enough tape cartridges or tape drive heads that some of your cartridges actually have a tiny bit  more usable space on them.  Keep an eye on your soft/hard errors counts for both the media and the drive.  Running some extra cleaning cycles or running vendor diagnostics on the tape drive may help also.

Jumping to LTO5 might be a wise move as that still allows you to read & restore your existing LTO3 cartridges.  If you jump to LTO6, then you cannot read your old tapes.  You will possibly also be switching from parallel SCSI to SAS when you upgrade tape drives.  Just make sure that you use a SAS HBA that supports tape.  Generally that means simple (non RAID) cards, unless it is listed as supported at http://www.symantec.com/docs/TECH70907

[pkh]

SW & HW compression gives roughly the same result so there is not much point in investigating SW compression if HW compression is working

[Larry_Fine]

SW & HW compression gives roughly the same result

"roughly" being a key word, especially since he seems on the cusp of making things fit.

[pkh]

Is there a guarantee that SW compression will definitely 100% fit his data onto one tape? If not, what is the point of investigating SW compression?

[Larry_Fine]

It was a suggestion to the OP and phrased as such.  Lighten up.

[pkh]

How do you like to be sent on a wild goose chase?

[IanW82]

Thanks for the replies, I actually tried switching to SW compression a few weeks ago and it actually made it worse so the HW compression is obviously a better option for me right now. 

An earlier suggestion on the tapes looks like it could be on the money, the last few few days I have used a brand new tape each day and it has been fine, no issues! I will keep this up to make it up to a week and asess it then. 

[IanW82]

Just to close this off, the new tapes worked for a few days but we must just be on the cusp, the last 10 days or so I have just been letting it run on to a second tape, easiest solution as far as I can see until we make the move to LTO5. Its a pain as once the second tape goes in it finishes within minutes! 

Thanks for the replies.

Ian