Hello Balanand,

There is no parameter per se in Solaris 8 & 9 (the ones that I use).  But
there are several parameters in Solaris that relate to # of bytes which can
be read in a single I/O call.

The maxphys kernel parameter limits I/O in the SCSI layer within the kernel.
Default is 128k.

We are using Solaris Volume manager; within the SVM layer there is a
md_maxphys kernel module parameter that limits within that subsystem.  If
not specified then it defaults to maxphys.   There is a corresponding
parameter if you are using Veritas volume manager, but I am not sure what it
is vxd_maxphys   or something.   Can someone else confirm ?

SD (scsi) devices used the cd module and they describe a sd_max_xfer_size
parameter that limits max I/O size within that type of device.  Default is
1MB

SSD (fibre channel scsi) devices used the cd module and they describe a
ssd_max_xfer_size parameter that limits max I/O size within that type of
device.  Default is 1MB

Hope this helps..

Jason Harris


-----Original Message-----
From: PINNI, BALANAND (SBCSI) [mailto:bp3965 AT SBC DOT COM]
Sent: Thursday, February 05, 2004 4:45 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: MAX_IO_SIZE on AIX


Can any body tell me how to find out the MAX_IO_SIZE in solaris?


===============
Answer:
===============

The "maxphys" kernel parameter limits the max. I/O size in the SCSI layer.
Default is 128k.
The "vol_maxio" kernel parameter limits the max. I/O size in the VxVM layer
(if installed). Default is 256k.
The "md_maxphys" kernel parameter limits the max. I/O size in the
DiskSuite/SVM layer (if installed). Default is equal to maxphys.
The "sd_max_xfer_size" module parameter limits the max. I/O size in the SD
module (if installed). Default is 1 Mb.
The " sd_max_xfer_size" module parameter limits the max. I/O size in the SSD
module (if installed). Default is 1 Mb.

There is a good doc on I/O size limits in the following Technote :

-- 08-02-2002

Set the default max. I/O size in Veritas to match/exceed the max. I/O size
that will be used.

in /etc/system, place

set maxphys=1048576
set vxio:vol_maxio=2048
* to allow 1MB I/Os.

vol_maxio is in Veritas units i.e. disk sectors of 512 bytes.
maxphys is in bytes.

We used to have exactly the same issue with DiskSuite, BTW, and needed
to set md:md_maxphys in /etc/system.  However, I understand DiskSuite was
modified to check the kernel maxphys value and use that to override
md_maxphys
if it was larger.  It is convenient to only have to turn one knob.

-----Original Message-----
From: Russell Brooks [mailto:rbbdsb AT earthlink DOT net]
Sent: Thursday, February 05, 2004 6:15 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: MAX_IO_SIZE on AIX


Hi,
  We using ADSM and RMAN to backup our databases.  I've run across a tuning
recommendation dependent on max_io_size.  AIX does not appear to have this
parameter, though it has been suggested that maxpgahead may provide similar
information.  Does anyone have information on correlation of these two
parameters?  Any insights from people who've been down this path would be
appreciated.

Thanks,
Russ Brooks
rbbdsb AT earthlink DOT net