Re: Performance difference between 2 machines

Matthias Hoys wrote:

> Regarding the AIX filesystem block size : when I look at the properties of
> our enhanced journaled filesystems (JFS2), the unit size = 512 bytes and the
> filesystem block size = 4096 bytes. So what's the difference between unit
> size and block size ?

Block size is the IO size any file system IO operations will always use.
The unit size is the minimal space allocation of the file system. Kinda similar to the old Windoze file system sector size: the minimal amount of space the file system will allocate to a file/inode-entry. In file systems with no provision for "unit size", it defaults to the block size.

> One of our 8.1.7 DWH databases (which needs to be migrated to Oracle 10g)
> has a block size of 16k, so what would be the reason for this ? (it was
> installed a long time ago by an external consultant).

Traditionaly, DWH consultants use a db block size of 16K.

> Is there any way to estimate the optimal block size for an existing database
> ?

None, other than benchmarking of your specific case. There are however guidelines based on past experience. They seem to point to 4K in AIX/JFS. But with JFS2 I'd probably be inclined to use 8K.

But NEVER make db block size less than file system block size. Ie: 2K db block size on a 4K file system is a BIG no-no. Received on Tue Jun 21 2005 - 20:07:37 CDT