Problem using iSCSI and Storage Foundation 5.0MP3

It's not possible to force the disks to be discovered in a particular order. However, if you want the order to remain the same after reboots, refer to the following links to set persistent naming:

VxVM 5.0MP3 (Solaris) Administrator's Guide - pp 106-108
http://sfdoccentral.symantec.com/sf/5.0MP3/solaris/pdf/vxvm_admin.pdf

html versions of relevant sections:
Changing the disk-naming scheme
http://sfdoccentral.symantec.com/sf/5.0MP3/solaris/html/vxvm_admin/ch02s05.htm

Displaying the disk-naming scheme
http://sfdoccentral.symantec.com/sf/5.0MP3/solaris/html/vxvm_admin/ch02s05s01.htm

Regenerating persistent device names (for explanation of impact/implications of persistent naming)
http://sfdoccentral.symantec.com/sf/5.0MP3/solaris/html/vxvm_admin/ch02s05s02.htm

The following technote is also helpful (refers to 4.1 but still applicable to later versions)
TN 278998: VERITAS Volume Manager 4.1 persistently labels disk devices. The 'vxdisk list' command will no longer reflect underlying OS device name changes
http://seer.entsupport.symantec.com/docs/278998.htm

This still won't guarantee/cause the disks to be picked up in the same order across both systems though. To match up, use vxdisk -e list to display the underlying OS name to match up manually.

If the names absolutely must match on both nodes, you can try the following unsupported workaround/hack to the disk.info file. Note this is not supported so it's at your own risk, and any new disks added later may/will still be in different order.

1. If VCS is running, freeze any service groups that have volume manager resources (preferably stop VCS all together/do this in an outage window as it's entirely possible this could lead to outage if there are errors in the file/any problems)
# hagrp -freeze <group> ### repeat for all groups with volume, dg, etc resources
2. Ensure persistent naming is on/enabled
# vxddladm get namingscheme
3. Back up the /etc/vx/disk.info file
# cp -p /etc/vx/disk.info /other/tmp/location
4. Edit the disk.info file to so the disks in the desired order. Ensure there are no duplicates/no typos in the file - ie: try to limit edits to the numbers to avoid introducing any errors
5. Restart vxconfigd using vxconfigd -k or reboot the server
# vxconfigd -k
6. Unfreeze any groups that were frozen in step 1

Note: for the issue of DMP only seeing one device instead of eight, have you checked if your configuration/settings are supported in the HCL/Hardware technote? If they are listed as supported it may be worth logging a case to see why the disks aren't displaying correctly with DMP enabled.

Hardware Compatibility List for SF HA 5.0 [...] - http://support.veritas.com/docs/283161
ftp://exftpp.symantec.com/pub/support/products/Foundation_Suite/283161.pdf

SF HA Hardware TechNote for 5.0 MP1 and 5.0 MP3 (AIX, Solaris)[etc] - http://support.veritas.com/docs/283282
ftp://exftpp.symantec.com/pub/support/products/Foundation_Suite/283282.pdf