quantity of tape capacity reduction

[Wolfgang_Beyer]

I obtained a warning saying that due to some problems the capacity of a tape has been reduced but no data are lost. Due to some subsequently tape capacity overflow it seemed to be >10GB for our DTL IV 40/80GB tape. Is there any possibility to get precise information about the quantity of capacity reduction?

Thank you for any information

[Rucha_Abhyankar]

Hello,


The reduced capacity may be reached while trying to backup already compressed data.


Check whether hardware compression is enabled.


If you were to backup already compressed data, it shall not perform any further compression.


Check for Event IDs 7,9,11,15.


Set the tape drive SCSI ID as low as possible, avoiding 0 or 1, which are usually reserved for bootable devices.


NOTE: If we do not receive your reply within two business days, this post would be marked assumed answered and would be moved to answered questions pool.

[Madhuri_Shenoy]

As per our previous reply, marking the case as "assumed answered" and moving it to "answered questions" pool.

[Wolfgang_Beyer]

I should mention that I obtained this warning in the protocol file not during the phase of writing data on tape but during the subsequent identity check.

In the meantime I tested the capacity of 4 tapes saving 100MB files (exactly 100*2^20Bytes) containing random numbers until tape overflow. According to this test on 4 tapes I measured capacities of 28100, 26700, 26700 and 26500MB. The tape with 26500MB was one for wich I obtained earlier such a capacity reduction warning. Does that mean, that it is only a minor tape capacity reduction? By the way: It is strange, that the capacity is different for nearly all tapes. And furthermore: It is strange that the physical capacity of 40GB tapes is actually close to 27GB only.

Is it a permanet capacity reduction at all? Does it has to do with defect parts of tape wich are marked to be no longer used in the future?

What do you mean by compressed data? I did'nt saved special compressed data but an usual mix of data of many persons containing also "compressed" data like JPG-images from a NTFS partition but without the NTFS compress option activated. Hardware compression of the tape drive was enabled.

The tape drive has its own SCSI controller and ID=1 is used for the robotic device and ID=2 for the tape drive itself.

[Ajit_Kulkarni]

Hello,

As mentioned in the reply given by Rucha, this warning may come while trying to backup already compressed data.
So ensure that files you are backing are compressed.

To know more about the tape capacity and the compression, please refer to the following technote:

Backups fail to get double the amount of the native capacity recorded to a media, even when hardware compression is being utilized.
http://support.veritas.com/docs/199542

Hope this helps you.

Regards


NOTE : If we do not receive your reply within two business days, this post would be marked "assumed answered" and would be moved to "answered questions" pool.