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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Max phy I/O size on Hp-UX
As per the HP docs, MAXPHYS can be >= (64K or 256K) and HP silently enforces it. ( Note the >= ). It could depend on whether the hardware supports it. We are using V-Class servers and here is a reference to it in one of the header files.
scsi_ctl.h
/* ** Size of SCSI Passthrough I/O Requests **
I had done some testing sometime back and the values I obtained (p3) suggested a 2M value. I think HP would have silently split the IO into more than one IO.
Thanks,
Denny
Prasada.Gunda1_at_hartfordlife.com wrote:
>
> 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
-- Denny Koovakattu http://www.oneco.net/ _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Denny Koovakattu INET: denny_vk_at_yahoo.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Thu Mar 22 2001 - 16:57:37 CST
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