| Author |
HP StorageWorks AIT2 50/100GB
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| Toolmann 2005-01-27, 8:45 pm |
| I am unable to achieve much more then 1.2:1 compression ratio on my
backups. I run Windows 2000 and use Veritas Backup Exec 9.1 and a
mixture of Compaq 50/100 and Sony SDX2-50C 50/100 tapes. I have tried
compression settings of "hardware first, then software" as well as
"software only".
Any help would be greatly appreciated.
| |
| Maxim S. Shatskih 2005-01-27, 8:45 pm |
| Maybe you backup uncompressable data?
--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
maxim@storagecraft.com
http://www.storagecraft.com
"Toolmann" <davidrearly@hotmail.com> wrote in message
news:1106871115.858181.283940@z14g2000cwz.googlegroups.com...
> I am unable to achieve much more then 1.2:1 compression ratio on my
> backups. I run Windows 2000 and use Veritas Backup Exec 9.1 and a
> mixture of Compaq 50/100 and Sony SDX2-50C 50/100 tapes. I have tried
> compression settings of "hardware first, then software" as well as
> "software only".
>
> Any help would be greatly appreciated.
>
| |
| Toolmann 2005-01-28, 7:45 am |
| I am backing up a mixture of MS Office documents, PDF's and pictures.
I think I should expect a little better compression such as 1.5:1 but
maybe I am wrong.
| |
|
| Compression on tape drives is a lot harder than software compression a
la ZIP. It has to be done in real time, and every block has to be
compressed separately so you can access it individually. As a result,
the compression factors are lower than what you're used to.
| |
| Maxim S. Shatskih 2005-01-28, 5:45 pm |
| PDF is very bad in terms of compression.
--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
maxim@storagecraft.com
http://www.storagecraft.com
"Toolmann" <davidrearly@hotmail.com> wrote in message
news:1106919138.812278.292640@z14g2000cwz.googlegroups.com...
> I am backing up a mixture of MS Office documents, PDF's and pictures.
> I think I should expect a little better compression such as 1.5:1 but
> maybe I am wrong.
>
| |
| Maxim S. Shatskih 2005-01-28, 5:45 pm |
| > Compression on tape drives is a lot harder than software compression a
> la ZIP. It has to be done in real time,
Yes, and also memory is usually scarse. You cannot run PPM algorithm on a
drive, and I even have doubts you can run BWT there (due to unpredictable time
degradation on "bad" data). So, only LZ, which is the bad algorithm for any
well-compressable data.
--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
maxim@storagecraft.com
http://www.storagecraft.com
| |
|
| PPM or BWT sure would be cool but I don't think anybody has designed
silicon for them (yet?). LZ seems like the only game in town today.
| |
| Anton Rang 2005-02-02, 5:45 pm |
| "Maxim S. Shatskih" <maxim@storagecraft.com> writes:
>
> Yes, and also memory is usually scarse. You cannot run PPM algorithm on a
> drive, and I even have doubts you can run BWT there (due to unpredictable time
> degradation on "bad" data). So, only LZ, which is the bad algorithm for any
> well-compressable data.
The ALDC (Adaptive Lossless Data Compression) algorithm is an ECMA standard:
http://www.ecma-international.org/p...ST/Ecma-222.pdf
It uses a history buffer no larger than 2K, so even as LZ compressors go, it's
very modest.
-- Anton
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