Here is some information I found on various Solaris sites. It's quite long, but covers this topic fairly well. I have posted a summary of what I think is your problem at the bottom:
Solaris boot process consists of two conceptually distinct phases, primary boot and secondary boot. The primary boot is implemented in the BIOS ROM on the system board and in BIOS extensions in ROMs on peripherial boards. The code is x86 real-mode code. This part of the boot process is common for all PC-compatible systems.
A Solaris boot partition is a primary partition, and must be active in order to boot Solaris. It begins with one-cylinder boot slice, which contains the partition boot program pboot in the first sector, the standard Solaris disk label and the VTOC in the second and third sectors, and the bootblk program in the fourth and subsequent sectors (VTOC is discussed later).
When a system is booted from a hard disk drive, MBR of that disk is read into memory. If Solaris was the last operating system installed to this disk, its MBR contains mboot - master boot program. The program, though specific for Solaris, works as usual Master Boot Code, that is, it reads the first sector of the first active primary partition on the boot disk, and jumps to its first byte. If the active partition is Solaris boot partition, its VBS is read and pboot - partition boot program contained there is invoked. Then pboot in turn loads and runs bootblk program.
In case Solaris is booted from floppy or CD-ROM, the first physical sector of the media read by BIOS, is a VBS not MBR. The pboot program contained there is responsible for loading the image of the boot manager strap.com.
VTOC
A disk label or Volume Table of Contents (VTOC) is a special area of every disk set aside to store information about the disk controller, geometry and slices (partitions). The interactive format(1M) or the commands fmthard(1M) and fdisk(1M) can be used to create a VTOC.
The definition of a slice consists of 5 files: slice number, tag, flag, starting sector and size. There is room for 16 slices per partition. VTOC occupies the second and third sector of the Solaris partition.
Summary:
With this information, and my (sometimes painful) experience with Compaq servers, I think it's safe to assume that you need a disk controller driver for Solaris. If the machine has a RAID controller you may not be able to get this working.
The nearest I have come to this situation was when my company bought a DELL PowerEdge with a RAID controller. We had to disable the RAID and use the Adaptec SCSI drivers instead, to run Solaris for Intel.
I haven't tried installing it on a Compaq server - so I'd be interested in your solution.
I hope this helps.
