how many factors will affect the filesize of db2 full backup image?

[e***@mofcom.gov.cn]

Now I am implementing full offline backup of my database using tsm. But in this case TSM is out of space and report errors. I checked the images for latest several full backups and found that there is big gap in filesize among these images, for example, the filesize of some images is about 26G and others are about 70G. Every time I reorg all the user tables before backuping. I make some statistic about the tablespaces and find that the total size of used pages is about 26G multiplied by pagesize, while, the total size of high water mark is about 70G multiplied by pagesize.

So my question is :
1 what is the internal mechanism of db2 backup?
2 how does tablespace affect the filesize of backup, such as used page and high water mark?

[Kelly Rodger]

Can you please post which version of DB2 you are running?

The backup utility may try to read all pages up to the current high-water mark, but will not backup extents of pages which it knows for certain to be unused. In order to be certain that free space has been fully reclaimed I might suggest that a LIST TABLESPACES SHOW DETAIL command be run after your REORG(s) complete.

http://www.ibm.com/support/docview.wss?uid=swg21006526

Cheers.
Kelly Rodger

[e***@mofcom.gov.cn]

Dear Kelly Rodger,

Firstly I want to say thanks to you for your kindly help.

I have DB2V8+fp14 running on AIX5.3.

here is a database with dpf.

the result of backup for partition0 and tablespace information are as the following:
total size of used page is about 27.7G and the total size of hwm is about 46.8G. I have two backup images of Partition0 having several 2 days period. the file size of image1 is 28.9G and the other is about 50.5G. After reading your reply I seem to know the gap(21.6G) between the two images is the extents of pages which db2 knows for certain to be unused, maybe because of reorganization. right?

[Kelly Rodger]

Yes, that would certainly be possible.