Tape Capacity

[Beryl_Tesler]

I am using an HP SureStore Dat 40x6 (Robotics Tape Drive) and have been experiencing NO Compression on some of my backups. I have them set to Hardware otherwise software and the best I get is 1.25 on incrementals, but nothing on Full Backups. This is a problem and I haven't been able to find a way to correct it. I have replaced all the tape (DDS-4mm) with new ones. The drive is cleaned weekly. Anyone have an IDEA?

Thanks

[Sharvari_Deshmu]

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 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.

For further information, please refer the technote below:
http://seer.support.veritas.com/docs/199542.htm


Thanks,

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[Beryl_Tesler]

Thank you for your quick response. I have played with these setting and do understand that compression would differ with different file types. But, I am getting ZERO compression for the whole backup, or at best 1.07:1, which is practically the same, of no value. I am going to try it again with Hardware, else software and if that does not work, I will try Software alone. The only backup that is an issue is the NON Incremental. The Incremental is backing up with 1.25+:1, which works also since I am not looking at the smae quantity of data that needs to be backed up.

Thanks,
Beryl

[priya_khire]

Hello Beryl ,

It seems you get 0 compression on the Full backups. What device are you using for the backups? Does it support compression? If it does, only then will the hardware compression be effective.

Check if you get any device related errors in the event logs. Refer to the following technote which might be helpful:

Compression Ratio does not display or displays incorrectly when using software compression.
http://support.veritas.com/docs/273089

Revert with details if the issue persists.

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Regards.

[Beryl_Tesler]

Please see first entry for hardware/Equipment details.
I checked the event viewrand there are no indications of tape errors. The properties of the HP drive are correct, as per Veritas documentation. If you think using software compression will help, then I am for that. These tapes are only used with Veritas.

Thanks

[Renuka_-]

Hello,
Please check if you have the same problem with Software compression, please note that hardware compression is done by your tape, hnece it should be supported by the tape itself.
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[Beryl_Tesler]

I tried Software compression and it increased from 21gb to 25gb. This is certainly better but not nearly any multiple of the 20gb native. It would be much better to get at least at 50% bump rather then a 25% bump. This would indicate to me that the next version of a hardware solution needs to be greatly oversized since compression is mostly a pipe dream. If you have any further suggestions on improving the compression I would like to know

[Ken_Putnam]

since compression is mostly a pipe dream

Exactly. 2:1 compression is a Marketing dream, not an Engineering promise.

When setting up a new server, I use 1.3:1 as a rule of thumb until several backups have completed. Some get better, some worse.

[Deepali_Badave]

Hello,

Upgrade the firmware of the device and drivers of scsi controller.


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[Beryl_Tesler]

Ken,

I think your responseo is the most realistic I have recieved. I think between the Hardware and the software there is some conflict that doesn't allow maximum compression. Everyone always points a finger at the other vendor. I am getting about 25% compression and I think that is about the best I can do. I will either have to rethink how I do backup on this unit or upgrade my unit to a much higher capacity. am going to have to go way over size on the backup. Thank you for your help.

[Beryl_Tesler]

Thank you for your help. I am going to assume the best I can get out of the combination of hardware and software is only about 25-30% compression. I do not think that either your compression or that of the hardware will impove much beyond that. Any honest compression factor would benefit the user in making a determination on the size of the unit needed to meet the needs for an extended period of time. You might consider that in the future