Soft Errors and Wasted Tape Capacity

[Wendell_Crouse]

Hello

I run a full backup job that has started outgrowing a single 100-200 GB tape. Surprised, I looked to see that I was showing a negative compression ratio of 0.617:1. Writing 60GB of data is taking 98GB of tape! Looking closer, I also see 600 plus soft read errors.
Hardware compression is enabled.
I'm using the latest Veritas drivers.
The tapes are new this month.
My scsi card is an Adaptec 29160LP.
The drive is an HP LTO Autoloader C7145.
Is my driving waiting for data or timing out? What should my scsi settings be?
Thanks

[Sharvari_Deshmu]

Hello,

Please check whether the device is "tested" in the list below, if yes then please install latest veritas drivers from the link below:
http://support.veritas.com/docs/271383


VERITAS Backup Exec (tm) 9.1 - Device Driver Installer (20050115) - Includes Tape Driver Release (20041231) and Robotic Library Release (45) (Intel Only) http://seer.support.veritas.com/docs/273853.htm

If not tested then please install latest manufacturers drivers and then verify the result.

Also please check the device configuration with the help of the technote below:

How to troubleshoot issues with a Robotic Library or Tape Drive in Backup Exec 9.x and 10.0

http://support.veritas.com/docs/255501

Please update the firmware of the device


Thanks,

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.Message was edited by:
Sharvari Deshmukh

[Wendell_Crouse]

Thanks for your reply.

My Drive is listed as 'Tested'.
I am running the latest version of Veritas' drivers.
The firmware of my drive is at the latest level.
My Event Log is clear.

As an additional note to my problem, it appears that my daily differential backups, each less than 10 GBs and on its own tape, are showing compression. Only my weekly full backup is showing excessive size and negative compression. As a test, I put the existing job on 'hold' and recreated a new job for the full backup. Same deal. Negative compression. There is nothing unusual about this data. An Exchange database job runs separately.

wcrouse

[Deepali_Badave]

Hello,


When using compression it is important to remember that the 2:1 compression ratio frequently assumed or stated in technical documentation is an ideal and seldom reached as a practical average.

Some files compress better than others. Text files are probably the most compressible files in general while high density graphics files like files with .jpg, .gif, .zip, or .cab extensions are not likely to compress at all. Also, many programs, including some database and mail programs, already compress the files they control.

The incorrect media capacity problem is usually observed on tape devices which do not have Media Capacity Checker functionality. Generally, for most of the tape devices, this functionality is initiated from the firmware of the tape device. Even though the tape capacity is reported incorrectly, during the backup operation, the entire media capacity should be consumed.

Total capacity of the media that is currently loaded in the device. If a tape device supports reading of the total capacity amount, then Total capacity is derived from the total capacity amount. Otherwise, Total capacity is estimated based on past usage of the media. Perform a full backup until the tape is filled, for example if the tape capacity is 50 GB then perform a backup of 50GB with overwrite option. Once the backup is completed and next time when the tape is inserted for backup, check the media capacity displayed.
Media capacity is calculated based upon past experience, once a tape has been read from beginning to end via backups to the tape and then when the tape is overwritten afterwards; or from a long erase or full catalog job.

Hence we request you to perform an erase operation on the tape and check. Also perform a full backup until the tape is filled for example if the tape capacity is 160GB then perform a backup of 160GB with overwrite option. Once the backup is completed and next time when the tape is inserted for backup, check the media capacity displayed.

To diagnose the cause of issue please cross-check the compression ratio from Windows's native backup utility (ntbackup) with hardware compression(if supported by tape device)enabled. Select the same type/amount of data to backup and observe the result.

The following can also affect hardware compression:

1. The tape drive may be trying to compress data that is already compressed. If the data cannot be compressed any further than it already is, the attempt may cause the data to expand. Run a test backup with no compression to compare how much data can be written to the tape media without compression. When using hardware compression, software compression should be turned off, and vice-versa.


2. The system may not be able to keep up with the tape drive. If data is sent to the tape drive at a rate that is either slower or faster than the rate at which the tape drive can write the data to the tape, then the tape device must stop and wait for the computer. Each time the tape drive stops, it writes tracks of undefined data (gap tracks), repositioning the read/write heads for the time when more data becomes available. This causes the tape drive to stop and restart frequently, affecting tape capacity.

Also refer to the following points.
1) Stop the Removable Storage Service and then try to perform backup.
2) Avoid using SCSI ID 0,1 and 6 for tape 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.