No and yes. What I mean is, the DB_Block_Size is a parameter that you set when creating the db, so it can be anything. But, in order to have efficient I/O and storage on your disk, it is a good idea to select a block size that is in line with the OS buffer.

For example, on linux, the default buffer size is 4K. So, if you set a db_block_size of 2K you would immediately double the amount of disk space that is required. This is because each time Oracle writes to the disk, it will only flush half a system buffer to the disk. The other half would be empty. Alternatively, if you set the db_block_size to 8, every time you need to read something from disk in Oracle, the file system will have to make 2 disk reads!! Note that I stress by default. It is possible to change the system buffer size on installation of the OS.

Also, this isn't applicable to Windows OS or if you have used raw partions for your Oracle datafiles. This is because you would then be using direct I/O. There is no file system buffer to contend with and you can have any DB_Block_size that you like when creating the DB. I normally pick a block size of about 16K.

Also, I know that in 9i there is a feature that allows you to have multiple block sizes. Unfortunately I haven't played with it. I have heard that in Oracle 10g that the block sizes are handled internally.

Mace

>Hi, Macer
>thanks for your prompt reply
>the DB_Block_size is depends on OS right...?
>
>Best Regards
>Mazahir