StoreEver Tape Storage
cancel
Showing results for 
Search instead for 
Did you mean: 

HP Storageworks Dat 72 Tape full at 42

 
SOLVED
Go to solution
Highlighted
New Member

HP Storageworks Dat 72 Tape full at 42

I don't understand why i can't fit more than 42 gb on this 72 gb tape. I have Symantec Backup Exec 10 with windows server 2003. I ran the HP L&TT and is says "hardware compression algorithm is switch off, probably set by your backup software, L&TT has not altered your setup." But it states in the test that compression is at a ratio of 2.15:1. When i try to do a full backup, it spits the tape out after abour 42 gb and wants another one isntered. Why can't I get close to 72 gb on a tape?
6 REPLIES 6
Highlighted
Trusted Contributor

Re: HP Storageworks Dat 72 Tape full at 42

Denyse if it makes more than 36GB then tape drive is making compression however I haven't seen any tape with the full 72GB this is because data cannot be compressed any further.

Pablo Alvarado Siles
Pablo Alv Siles
Highlighted
Respected Contributor

Re: HP Storageworks Dat 72 Tape full at 42

TDK is right that you are getting compression on your backup job, or you'd only be able to fit about 36GB +/- .

Different data is compressible different amounts. Did you scan your entire disk to get the 2.15:1 ratio? Exactly which test did you run?
--
Liberty breeds responsibility; Government breeds dependence
Highlighted
New Member

Re: HP Storageworks Dat 72 Tape full at 42

In HP L&TT i selected my tape drive and pressed the big Test (checkmark) button on the toolbar, Configuration - Test Group - Data compression test.
Test results said "Data sent to DC: 65664 Kbytes, Data written to tape: 30508 Kbytes, Write compression ratio is 2.15:1."
Highlighted
Frequent Advisor

Re: HP Storageworks Dat 72 Tape full at 42

Ok, that explains it. This test sends a testpattern, not real data.
This test data is very highly compressible so you see this whopping 2.15:1 figure.

When backing up regular data of a general mix of different office files (texts, docs, spreadsheets, etc. you'll see more like 1.8 in practice.
When the backup contains lots of graphical files, JPGs, PNGs, PDFs, videos, etc. in most cases you're lucky to get higher than 1.0, many of these file formats are already so much compressed that no further compression is possible.

Have a look at the type of data you're sending to the tape; that should give you an indication what to expect.
Highlighted
New Member

Re: HP Storageworks Dat 72 Tape full at 42

Okay, i see. Thanks.

But what i am having trouble comprehending is why 42 gb = full on a 72 gb tape.
The tape can fit 36 gb compressed or uncompressed data? Where does my extra 6 gb come from? and why is it no more or less? Is only compressed data allowed on the tape or can both compressed & uncompressed be simultaneously?
Highlighted
Frequent Advisor
Solution

Re: HP Storageworks Dat 72 Tape full at 42

The physical capacity of the tape is 36Gb.
You loose a bit in overhead.
Data is compressed while writing to the tape.
Compare when you create a ZIP or RAR from random data. If you do that for things like JPG or MPG files, then you may even end up with files that are larger than the original as also the compression process does require some overhead to recover the original data.