MAX_IO_SIZE

[Jeet Arora]

Hi

How do I find out MAX_IO_SIZE. I am on
HP-UX eccdb999 B.11.11 U 9000/800 261487694 unlimited-user license .

I tried kmtune but it does not have max_io_size as an option.

Thanks
Jeet

[Peter Godron · Accepted solution]

Jeet,
if you are thinking in Oracle terms:
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=804789

[RAC_1]

That must be related to file system. For vxfs you have soem options that you can tune, But before you do that, read the details crefully.

man vxtunefs

[Jeet Arora]

Yes, my question is related to Oracle. I have read all the links and am still confused. My maxphys is set to 1MB but looking at answer to one of the link I would think it should be 256K, since we are not using raw or direct I/O. Thanks for the reply.

$ kmtune -q scsi_maxphys
Parameter Current Dyn Planned Module
========================================================================
scsi_maxphys 1048576 - 1048576
eccdb489-

What is the maximum I/O size (MAXPHYS) nowadays on HP-UX and Solaris?
MAXPHYS has long been fixed at 64K on Solaris, and 256K on HP-UX. However, from Solaris 2.6 it is defined in /etc/system and defaults to 128K. On HP-UX 11 it now defaults to 1M. However, I think the LVM layer still constrains I/O operations to a single logical track group, which is 256K, so the higher MAXPHYS only applies if you are not using LVM, which is most unusual. Of course, these large physical I/O sizes are only possible if you are using raw or direct I/O. Perhaps more importantly, there is an internal Oracle kernel constant (SSTIOMAX) that limits I/O operations to 512K.