Env: DB2 8.2/AIX 5.3

A DMS tablespace size is 150 GB but only 1 GB is used. HWM and Pages used remains the same.

If a backup is taken, will it backup all 150 GB of tablespace or only 1 GB of the used space( or HWM whichever is high) ?

It will not backup all 150 GB that is allocated if HWM is 1 GB. But you should use the compression option on the backup command anyway. However, I am not sure if the backup will have to read the entire allocated space to find out if there are any pages to backup.

Thanks.

I did a quick test and it backs up only 1 GB. I increased the HWM level of tablespace and noticed that backup size/time increase proporionately.

I think the backup uses the HWM to find out how many pages to backup instead of reading all allocated space.