This question regarding max physical I/O size for hp-ux v11.
When we were talking to unix sys admin, she searched in HP knowledge base and found
that 256k is the maximum
physical I/O for hp-ux. When I was looking at Q&A on Steve Adams's web site, the
answer is 1M for max physical i/o
size for hp-ux.
Steve, Could you please let me know if I am missing some thing here.
>From Steve Adam's Web site:
Maximum I/O size
4 January 2000
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.
>From Knowledge base on HP Web site
What is MAXPHYS for HP-UX systems?
DocId: KBRC00003216
Updated: 7/31/00 7:37:00 AM
PROBLEM
What is the the maximum size of a single I/O (or MAXPHYS) that can
be issued to a device on an HP-UX system?
RESOLUTION
MAXPHYS is not a tunable on HP-UX systems but it defaults to 256KB.
This can be seen in one of the system header files:
1. vi /usr/include/machine/param.h
2. Search for MAXPHYS
This should return:
#define MAXPHYS (256 * 1024) /* Maximum size of physical I/O transfer */
So MAXPHYS is 256KB. This is not tunable to larger value due to driver
restrictions.
Thanks in advance for all your comments.
Regards,
Prasad
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