[SunHELP] Tuning "maxphys" and "vol_maxio" kernel parameters

[DAUBIGNE Sebastien - BOR]

Has anyone of you ever experienced tuning the "maxphys" and "vol_maxio"
kernel parameters ?

Here we have an E6500 running Solaris 2.6, with 8 JNI Jaycor FCAL HBAs
connected
to an EMC 3930 disk array.

Well, Sun and EMC have installed hardware and software components, including
the  fcaw driver module, so we had faith in them making every required
configurations 
in order to achieve maximum troughput.

Unfortunately, after reading the fcaw(7D) manpage, I doubt they did so : The
documentation
says the "maxphys" parameter, which determines the maximum SCSI I/O request
size, and 
defaults to 128 K should be increased to 8 Mb to achieve maximum bandwidth. 
This parameter was leaved to the default value (128K) on our E6500 !!

I'm afraid our system could be somewhat restrained.

Are there any hidden drawbacks or side-effects to change this value,
especially for non-fcal
SCSI devices (like the bootdisk)  ?

Should I also increase the VxVM  "vxio:vol_maxio"  parameter (default to 512
blocks = 256 K),
considering we exclusively access the EMC disks through VxVM ?

Any comments/experiences appreciated.

---
Sebastien DAUBIGNE 
sebastien.daubigne at sema.fr <mailto:sebastien.daubigne at sema.fr>  - (+33)
(0)5.57.26.56.36
Sema Global Services - AFM/DW/Pessac