topic Re: OS block size ??? in Operating System - HP-UX

OS block size ???

KY.Chuang — Thu, 13 Feb 2003 04:06:05 GMT

Dear all,
I have a question about OS block size?
where to set the OS block size? Is it 512 bytes(Default)?
and, does it have any meter which I renew the OS block size?

I want to set the OS block size, because I want to modify Oracle(8.0.5) block size when I create new databse.
Why I always create a Databse
,db_block_size it always set
2048 bytes? (My hope the db_block_size is 4096).

Thanks. K.Y.

Re: OS block size ???

Mani_3 — Thu, 13 Feb 2003 04:32:44 GMT

Hi KY

You can change the bock size while creating the filesystem using the mkfs_vxfs command.

In the mkfs_vxfs command their is an option bsize=n with which u can change the block size...following is an excerpt from the man pages of mkfs_vxfs

===========================
bsize=n, where n is the block size for files on the file system and represents the smallest amount of disk space that will be allocated to a file. n must be a power of 2 selected from the range 1024 to 8192. The default is 1024.
============================

Refer man mkfs_vxfs for futher info

As u said the default block size is 512bytes.

Hope that helps

Regards
Mani

Re: OS block size ???

Rajeev Shukla — Thu, 13 Feb 2003 04:42:49 GMT

See the block size can be modified when you create a filesystem which by default 1024. Now if you are using RAW Devices in Oracle there is nothing much you can do.

Rajeev

Re: OS block size ???

Christian Gebhardt — Thu, 13 Feb 2003 06:45:57 GMT

Hi

You have to set the db_block_size of a database in the init-file (init.ora).
This is an initial parameter you never can change for this database.
We have db_block_size=8192 in most databases.

Very important is that db_block_size is a multiple of OS block size.

Remember that you many other parameters depend on the db_block_size
db_block_buffers
db_file_multiblock_read_count
...

Chris

Re: OS block size ???

T G Manikandan — Thu, 13 Feb 2003 07:00:42 GMT

#df -g
displays the fragment size and the maximum possible block size.
you can find the current block size using

to find out the block size for vxfs
#fstyp -v /dev/vgxx/lvolX
f_bsize-->current block size

for hfs
#tunefs -v /dev/vgxx/rlvolX | grep bsize

The block size should have been specified at the time of creation of file system.

'bsize' option to the mkfs_vxfs command should create the reqd block size for the file system.

Oracle recommends the block size of the database to be the multiple of OS block size of equal to that.

check the file system block size using fstyp and then you can make the neccessary modification to the Oracle block size for the new database creation.

Thanks

Re: OS block size ???

monasingh_1 — Thu, 13 Feb 2003 21:34:45 GMT

What you are refering to is the filesystem block size not the OS block size.
I think there is nothing known as OS block size, and the 512 you are thinking is the disk block size which is the default block size used by du command.
file system block size can be set while creating new filesystem and "man newfs_hfs" or man newfs_vxfs" should explain that very well.