How to know the max_io_size of my hp unix system ?

[Eric Unix]

Dear Sirs

DB_BLOCK_SIZE x DB_FILE_MULTIBLOCK_READ_COUNT = max_io_size of system
So
How to know the max_io_size of my hp unix system ? Appreciatively.

Best Regards
Eric

[Sandeep_Chaudhary]

unix # cat param.h|grep -i phy
# define PGNDXWDTH (32-PGSHIFT) /* bit width of a physical page no
#define MAXPHYS (256 * 1024) /* Maximum size of physical I/O transfer */
* flag, callers such as physio() would compare the B_READ/B_WRITE flag in t


here look foe MAXPHY parameter. It talks about max physical IO.

[Eric Unix]

Hello Sirs

There are much param.h files in our system, and which one is right one ?
Thanks in advance for your kind help.

Best Regards
Eric

[Eric Unix]

Hello Sir

Have check the file, and it look as follows
# define NBPG_PA83 2048 /* 2k page size for PA-RISC 1.0 */
#endif /* not PGSHIFT */

#define MAXPHYS (256 * 1024) /* Maximum size of physical I/O transfer */

#define _BIG_ENDIAN /* Memory storage (bytes in word) */

so, seems no any setting in there, just only some comments in this file.

Best Regards
Eric

[Duncan Edmonstone · Accepted solution]

You are looking at C header files.

A "#" symbol does not represent a comment in these files. So if it says:

#define MAXPHYS (256 * 1024) /* Maximum size of physical I/O transfer */


Then you know that the Max size of an IO transfer is 256KB.

But don't try to change the file - you can't change this it's merely reporting hard limits in the kernel and drivers... the header file is merely a way for the system to tell C code what this maximum value is.

Waat are you trying to do here? The equation you first posted makes little sense to me in that for me it should really read:

DB_BLOCK_SIZE x DB_FILE_MULTIBLOCK_READ_COUNT must not exceed max_io_size of system

The two certainly don't have to equal each other.

Unless you are configuring a fairly major DSS style Oracle data warehouse then I'd go as far as making sure my filesystem block size is equal to my DB_BLOCK_SIZE and leave the rest alone.

And if you are configuring a large data warehouse - well if you're asking these questions you're not really qualified to do it...

HTH

Duncan