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DDS5 Capacity

Hi All,

I have a DDS5 DAT72 tape driver, one would assume that with compression I would be able to back up 72GB of data.

I remember however, that DDS4 did not back up the full 40GB.

What can i realistically expect the tape drive to back up?

TIA
Gareth
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gareth629
Asked:
gareth629
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2 Solutions
 
dbruntonCommented:
36 Gb without compression and that's realistic

You only get 72 Gb if you get 2:1 compression and this is only possible if the data can be compressed by 2 to 1.

Complex binary files like jpegs will not compress 2:1
Database files will probably compress better than 2:1

The answer really depends on the data you are trying to back up.  If you didn't get 40 Gb with DDS4 and your data composition is still the same then you won't get 72 B with DDS5.
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dbruntonCommented:
That's 72 Gb and not 72 B.
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jhanceCommented:
The KEY speci here is "UP TO 72GB".  The "native" capacity of these tapes is 50% of the advertised capacity.  So a DAT72 will hold only 36GB for sure.  

The drive incorporates a compression scheme to attempt to achieve the listed 72GB figure.  The problem is that some data cannot be compressed.  Usually this is because it's already compressed.  ZIP, JPG, MPEG, MP3, and similar files are already stored in a compressed form and will NOT compress any further.  

So depending on your mix of file types, your true capacity will vary, as much as 2:1.
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gareth629Author Commented:
Thanks guys,


mostly database backup and word docs, so i am looking good for a good amount?

g
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dbruntonCommented:
Both those types usually compress well but you won't know for certain until you try the backup utility.
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