Input/Output error booting some kernels on large disks

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

I recently did a NetBSD 7 install on a pair of 14TB drives with GPT 
partitioning. The disks are partitioned like this:

        start         size  index  contents
            0            1         PMBR (active)
            1            1         Pri GPT header
            2           32         Pri GPT table
           34         2014         Unused
         2048    104857600      1  GPT part - NetBSD RAIDFrame component
                                 Type: raid
                                 TypeID: 49f48daa-b10e-11dc-b99b-0019d1879648
                                 GUID: c6775acf-756b-4cc9-8d57-35345ccff9e6
                                 Size: 51200 M
                                 Label: root1
                                 Attributes: biosboot
    104859648  27239905247      2  GPT part - NetBSD RAIDFrame component
                                 Type: raid
                                 TypeID: 49f48daa-b10e-11dc-b99b-0019d1879648
                                 GUID: b2d43f4f-4689-44de-b9f0-27c8130fc395
                                 Size: 12989 G
                                 Label: data1
                                 Attributes: None
  27344764895           32         Sec GPT table
  27344764927            1         Sec GPT header

There's a RAID1 of the two 50GB GPT partitions (index 1) and I put a 
disklabel on that to avoid GPT-on-RAID-on-GPT:

# /dev/rraid0d:
type: RAID
disk: raid
label: fictitious
flags:
bytes/sector: 512
sectors/track: 128
tracks/cylinder: 8
sectors/cylinder: 1024
cylinders: 81919
total sectors: 104857472
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0		# microseconds
track-to-track seek: 0	# microseconds
drivedata: 0

10 partitions:
#        size    offset     fstype [fsize bsize cpg/sgs]
 a:  83886080         0     4.2BSD   4096 32768    90  # (Cyl.      0 -  81919)
 b:  20969472  83886080       swap                     # (Cyl.  81920 - 102397)
 d: 104857472         0     unused      0     0        # (Cyl.      0 - 102399*)

root is raid0a and is FFSv1. The system booted fine until I put on a newer 
kernel (this is a non-uEFI install). I get open netbsd: Input/output error 
from the bootloader when booting the new kernel. The original GENERIC 
kernel still boots and a straight copy of the non-booting kernel also 
boots, so it's not a kernel problem. I also tried /boot from NetBSD 9.0 
and if anything this was worse. With the 9.0 bootloader, there's an 
additional 10-second pause between the primary bootstrap line and the 
/boot menu appearing.

--
Stephen