[Crash-utility] kdump on x86_64 - why not discover a scsi device?

Hi all, Can anyone tell me why a dump capture kernel cannot discover my root device? I'm using an x86_64 box. My 2.6.16 kernel can load either a 2.6.16 or 2.6.22 capture kernel and it can successfully find the root device. The system has /dev/sdba and /dev/sdb. I'm using a root on sdb. But when my 2.6.22 kernel loads either a 2.6.16 or 2.6.22 capture kernel that capture kernel cannot find /dev/sdb. Must be a configuration issue. Maybe involving some combination of CONFIG_KEXEC and CONFIG_CRASH_DUMP. But I don't see how those can affect disk discovery. Any ideas? -Cliff