DB size confusion

[rudra132001]

Hi ,

While checking the DB size using promon - option (5) the db size seen is around 60 gb but when I check the online backup size for this db , its around 2 gb !!! .. we are using -com parameter while doing an online backup but why is there so much of diff in sizes ??

One thing that I can think of is that there might be some unused extents defined in st files which might cause this diff ,, pls correct me if i am wrong ..

 

[TomBascom]

There are many possible reasons why the sizes reported by different measurement techniques will be different. They are all looking at the question from different points of view and with differing objectives.

The size which is most appropriate depends on why you want to know There's a big difference between estimating how much disk space you need for a copy of the db vs how much tape is needed for a backup. Motivation matters too - if you're looking to claim bragging rights for The World's Largest Progress Database you're going to pick something different from someone who is emphasize how tightly they can pack a disk.

 

[rudra132001]

Hi Tom .. thanks for the reply ,
we are planning to take an offline backup of the db and use this backup to create a new instance .. so wanted to estimate how much disk space will be required for the new instance..will it occupy 60 gb as in production , or will it be near to the size of the off line backup which is roughly around 2 gb ??

 

[TomBascom]

That depends on what .st file you use not the size of the backup.

 

[tamhas]

The key here is that the physical size of the database has nothing to do with how much data you have stored in the database. The backup is reflecting the actual data. For your new database, you can either use the same structure, which will take the same space or define a new structure that is smaller since you don't have nearly enough data to fill the space you are currently using.

Of course, there is a lot more that simply being big enough to the optimum design of a database structure. That is a whole dialog or consulting engagement on its own.