Backup Capacity

Posted on 2004-08-19
Last Modified: 2010-04-03
I use Backup Exec version 9 to back up my Windows 2000 server to a DLT IV tape drive.  My question is that yesterday, I set a job to back up 110 Gig of data, and it didn't fail.  Everything I have read says that DLT IV stores 40 uncompressed/80 compressed.
The files were mostly SQL Server backup files, which I thought were pretty compressed already.

What is going on here?

Also, I get about 200 meg per min backups on average.  Does this seem normal?

Question by:jagoodie
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Expert Comment

by:Pete Long
ID: 11841063
>>Also, I get about 200 meg per min backups on average.  Does this seem normal?

thats not bad - i get about 490 \mb a minute but Ive got an MSL library running over fibre so yours is not bad at all

>>My question is that yesterday, I set a job to back up 110 Gig of data

is this a full, incremental or differential backup?
LVL 32

Accepted Solution

LucF earned 100 total points
ID: 11841140
Hi jagoodie,

> The files were mostly SQL Server backup files, which I thought were pretty
> compressed already.
They can still be compressed a lot, the backups really are not heavely compressed. For a database, you can normally count on a 1:8 compression ratio.


LVL 22

Assisted Solution

dovidmichel earned 25 total points
ID: 11841150
The throughput is in the normal range.

The 80gb compressed capacity is set by the marketing department and not the tech heads. Realistically the compressed capacity is more like 41gb to 100gb all depending on the type of data. Data that is already compressed such as zip, jpg, mp3... will not compress, binary types such as exe, dll, will compress very little. On the other hand plain text files will compress a lot. Also even the same data broken up into small files will compress less because each file has overhead. So lots of small files will take up more space on tape than few large files. Bottom line it depends on the data.

There is another possiblitiy but it does not come up very often, and that is if the drive is having recoverable write errors. Because they are recoverable the errors are not reported, but because there are errors blocks of tape are marked bad and so capacity is reduced. In your case this is unlikely because it also causes poor performance and at 200mb/m your performance is fine.  

Author Comment

ID: 11841295
Thanks for the info guys.  I just stumbled on to the Media Sets page in BE, and found that our backups are compressing at 2.8:1.  Amazing.  Plenty of free space left.
Thanks again,

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