Re: OS Block Size - MS Windows NT

On Mon, 21 Feb 2000 17:01:01 -0500, "Tommy Nobl" <tnoble_at_lawaudit.com> wrote:

>Right, but how can I (or my DBA) determine what the lowest-best value for
>this setting would be under NT. For instance, under VMS, the OS block size
>is (or used to be) 512 bytes (and I think it cannot be changed), so the DB
>block size could be any multiple of that (i.e. 512 x 5 = 2560). I think you
>can set this database parameter however you like, but if you know the OS
>block size, you can set it most efficiently so as little disk space as
>possible is consumed by empty allocation.
>
>Am I making sense?
>

You certainly are.

The default memory PAGE size in NT is 4K. Given that the shared buffers in ORACLE use a similar mechanism to OS paging (although much less sophisticated), it makes sense to make the unit of I/O for the shared buffers the same as the page size. That way, if NT decides to swap out the ORACLE buffers, at least it is swaping-out integral buffers!

The block size for general file I/O can be anything you want (it's under control of the app, not the OS).

However, the unit of I/O that NT uses to satisfy any block read/write request is the partition's cluster size. Which can be set at different values at partition creation time. Either automatically in the case of FAT partitions, or as a selectable value for NTFS-formatted partitions. Note that even for NTFS, NT will try to change the default cluster size depending on the size of the partition, so it pays to check EVERY time.

So it makes sense to select a cluster-size that matches the NT page size and make the database block size at least as large as the cluster size.

IOW, use 4K for the cluster size in partitions that are gonna store ORACLE tablespace files. Then set the database block size to 4K or a multiple of 4K (that means 8K in NT, as I believe that is the maximum Ora block size in that platform- I may stand corrected here as this changes quite often).

HTH Cheers
Nuno Souto
nsouto_at_nsw.bigpond.net.au.nospam
http://www.users.bigpond.net.au/the_Den/index.html Received on Tue Feb 22 2000 - 04:29:34 CST