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Backup Compression Problem

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Ganesh.I
Occasional Visitor

Backup Compression Problem

Hi,

I have HP Sure store DDS-4, with Firmware revision C005. I am using Yosemetic's TAPEWARE Backup program for taking backup. Device is connected to the system running Windows-2000 server. Tapeware server installed in the same machine. I am able to take more than 30GB of in the same machine in to Tape with compression.

The Problem is, I have mapped a network share from another computer having large voulme of Uncompressed TIFF files. I am unable to write more than 18GB of (TIFF) data in a Single 40GB-Catridge even though the Hardware compression is enabled.

Can some one guide me how to go about this?

Thanks in Advance.

Regards
Ganesh.I















5 REPLIES
Jan Klier
Respected Contributor

Re: Backup Compression Problem

Can you clarify what you mean with 'uncompressed' TIFF files?

The TIFF fileformat in itself already contains compression - so if you refer to the fact that you haven't compressed the files with an additional compression program (such as Zip), then the problem is that TIFF data are already highly compacted and don't compress much more.

Keep in mind that the DDS4 cartridge only has a native capacity of 20GB - the 40GB can only be achieved with a 2:1 compression ratio. Writing already highly compressed data, such as TIFF files, you would expect to only fit about 20GB on the cartridge, which matches your description.
Ganesh.I
Occasional Visitor

Re: Backup Compression Problem

Hi Jan,

Thanks for your information. I am using 20Gb Tape, the compressed capacity is 40Gb. I went through the properties of TIFF files saved in my disk. there was a option in Imaging application to check the File compression standard, My TIFF files are already compressed using CCITT Group 4[2d]Fax standard.

I guess this is the cause of my problem, However if its 20Gb catridge, I should be able to store more than 19Gb right?

But the device asking for another tape, when it reaches 18Gb, Could you please tell me why this is happening?

Thanks
Ganesh
Leif Halvarsson_2
Honored Contributor

Re: Backup Compression Problem

Hi
Try to switch compression off. In some cases when backing up highly compressed data to a device with hardware compression on the data on the tape can increase rather then decrease.
Jan Klier
Respected Contributor
Solution

Re: Backup Compression Problem

Hi Ganesh,

Yes, there are reasons for only fitting 19GB or even 18GB on the cartridge.

As the other poster noted, compressing already compressed data can actually sometimes expand the date (due to the decompression information that needs to be stored in addition to the data). Turning compression off will take care of this.

The other factor is overhead your backup application incurs storing the data on the cartridge. Typically, the application has to save catalog data, and often also identifying header blocks for each file backed up. That adds a few bytes per file being backed up which is written to the tape. In particular if you have a very large number of small files, this can add up to some overhead that will reduce your available capacity.

Depending on the block layout used by your application you may also waste some tape capacity. Applications can run faster if they use a fixed block size, but that implies they waste about 50% of one block per file statistically, as the file length often doesn't align with the block size (this is similar to the waste that filesystem incur on hard disks for the same reason).

I am not familiar with the Tapeware application, so I can't comment on how much the 2nd and 3rd problem affect this particular application.
Ganesh.I
Occasional Visitor

Re: Backup Compression Problem

Hi Jan,

Nice explaination, Now I got it clearly, Thanks for your guidance.

Regards
Ganesh