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Compression Ratio different

Created: 18 Dec 2012 | 8 comments

Good morning,

We have problems against compression ratio with our backup exec 12.5.

There is one tape with compression ratio 1.9.1 and that is all right.

Rest of tapes is 1:4:

Compression type Hardware (if available, otherwise software)

Device: HP Ultrium 2-SCSI (compression enabled Block and buffer size 64 KB Write Single block mode and Write SCSI PassTrough mode enabled.)

Backup runs on newest update of BE 12.5

I hope anyone can help us.

Comments 8 CommentsJump to latest comment

Kiran Bandi's picture

Compression ratios being acheived on backups very much depends on the type of data being backedup. For example, Kind of text documents, Word files, Excels does compress well whereas video files like .mpeg, zipped files does not.

To my knowledge compression ratio of 1.4:1 is quite acceptable most of the times.

Beesve's picture

Thank you for your answer,

But we backuped the same content, and only one tape is backupping right.

It has backupped perfectly for a couple of months and now 16 of 17 tapes are full because of this problem.

The content we backup is very  compressable.

regards,

pkh's picture

It could be that there are errors on the other tapes.  This will result in more space used.  Check the statistics for your tapes for errors.

Have you tried using a new tape and check the result?

Also, use software compression and see what is the compression ratio.  The hardware and software compression ratios for the same set of data should be about the same.

Beesve's picture

Thank you for your reply,

No errors on tape. tapes are about 10 to 20 times used.

all of our customers have the same compression type. Hardware otherwise software. Is Software compression better? So I think that is not te problem. Media seems full.

pkh's picture

I am asking you to switch to software compression.  I am asking you to use software compression to check what is the compression ratio.  This is to eliminate the hardware as a factor in the compression.

Beesve's picture

Thankyou for your reply.

I have made a new selection list with 2,5 GB data for this test.

Old tape test:

Software compression: compression ratio 1:1

Readded the same tape to the drive. Tape is recognized as newly and get a new lable? that is very strange. I see that this is the first time that a tape s recognized as newly.

I set the backup to hardware otherwise software compression: 1.1:1

New tape:

Hardware otherwise software: 1.3:1

regards,

pkh's picture

When you use software compression and you look at the tape, the compression ratio is always 1:1 because the amount of data sent to the tape drive and the amount of data written is th same.  you got to look at the job log and work out the compression ratio.

Nitin_P's picture

Hi Beesve , 

If we are sure about no errors on tapes , check the status of hard read / write errors on the tape drive.I would think about cleaning the drive once and observe the hardware compression if that makes any difference. 

Ref : http://www.symantec.com/docs/TECH7363

The compression is being controlled by actual hardware itself and its affected by data being backed up.

Please try the clean operation and observe the compression.