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Compression ratio varies even though amount/type of data stays the same

Created: 24 Jan 2013 | 3 comments

Running Backup Exec 12.5 on a Windows Server 2003.

I have had an issue where one nights backup compression ratio is 1.7:1, but the next night (exactly the same amount and type of data) it reduces to 1.6:1. This unfortunately causes a problem as it fills the tape when only compressing at 1.6:1.

Is there any explanation / solution for this? I cleaned the drive yesterday and still had the same yesterday evening, and the tapes are all fairly new, only 4 months old with approx 170hrs use.

Thanks

Comments 3 CommentsJump to latest comment

Backup_Exec's picture

Hi

First of all ensure BE12.5 is fully patched up with SP4 and all updates after it using live update.

Once done ensure you uninstall and reinstall tape drivers using tapeinst.exe which you will find in C-program files-symantec-backupexec folder .

After doing that ensure you do good power cycle means power off the library and media server and then power on library first and wait for it to intiliaze and then once done power on media server

Hope that helps

Thanks

Sameer

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CraigV's picture

Hi there,

 

If compression varies between tapes, I'd suggest you check the tapes out for errors.

Check a tape that has less compression, and look for Hard Write Errors. Excessive HWE are an indication that the tapes are faulty.

Furthermore, you can back this up...get 2 tapes which differ in compression. Download the tape drive manufacturer's diagnostic utility and run a compression test against the tape.

Thanks!

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Larry Fine's picture

re: I have had an issue where one nights backup compression ratio is 1.7:1, but the next night (exactly the same amount and type of data) it reduces to 1.6:1.

Are you backing up EXACTLY the same data exach night?  or just SIMILAR data?

The differences between 1.6 and 1.7 are pretty subtle.  if you are backing up different data, even if it is the same type of data, I would assume that the data compresses differently enough to give s slightly different ratio.

Either way, BE has no control over the compression ratio received, so it is either a data source issue or a target (drive or media) issue.

If you find this is a solution for the thread, please mark it as such.