After spending way to much time on this today, I verified that at least on the CMD CQD Q-Bus SCSI controller versions that I have if I wanted the CMD CQD controller to report an MSCP disk size of exactly 891072 blocks to match the SIMH emulated RA81 disk size, I had to soft resize the capacity of the SCSI hard drive to be 2 blocks larger, i.e. a capacity of 891074 blocks. This is with the CMD CQD controller reset to the default configuration with the 'Z' configuration option. The behavior of Q-Bus SCSI controllers from other vendors will be different.
After doing that I verified that VMS on a VAX CPU, and also the 2.11BSD standalone disklabel on a PDP-11 CPU saw an MSCP disk size of 891072 blocks with the SCSI disk size of 891074 blocks attached to the CMD CQD Q-Bus SCSI controller. I then installed RSTS/E 10.1 on a SIMH RA81 and then did the equivalent of a dd from the SIMH RA81 disk image file of size 456,228,352 bytes to the SCSI hard drive of capacity 891074 blocks. Then the PDP-11 CPU booted RSTS/E 10.1 from SCSI hard drive attached to the CMD CQD Q-Bus SCSI controller. Sorry for the extra long message. Gory details below. If I don't add the details now I'll forget all the details myself tomorrow. Resizing the 9GB SCSI hard drive down to a capacity of 891074 blocks on a Windows PC using sg3_utils-1.37 (I seem to recall that previously I tried this with a newer version of sg3_utils and something didn't work right): C:\sg3_utils-1.37>sg_scan PD0 [C] HDS728040PLAT20 PF1OA21B PD1 IBM DDRS-39130D DC1B CDROM0 [Z] TEAC CD-224E 1.7A C:\sg3_utils-1.37>sg_inq pd1 standard INQUIRY: PQual=0 Device_type=0 RMB=0 version=0x02 [SCSI-2] [AERC=0] [TrmTsk=0] NormACA=0 HiSUP=0 Resp_data_format=2 SCCS=0 ACC=0 TPGS=0 3PC=0 Protect=0 [BQue=0] EncServ=0 MultiP=0 [MChngr=0] [ACKREQQ=0] Addr16=0 [RelAdr=0] WBus16=1 Sync=1 Linked=1 [TranDis=0] CmdQue=1 [SPI: Clocking=0x0 QAS=0 IUS=0] length=164 (0xa4) Peripheral device type: disk Vendor identification: IBM Product identification: DDRS-39130D Product revision level: DC1B Unit serial number: RE1X3474 C:\sg3_utils-1.37>sg_readcap pd1 Read Capacity results: Last logical block address=17849999 (0x1105e8f), Number of blocks=17850000 Logical block length=512 bytes Hence: Device size: 9139200000 bytes, 8715.82 MiB, 9.1392 GB C:\sg3_utils-1.37>sg_format --count=891074 --resize --verbose pd1 inquiry cdb: 12 00 00 00 24 00 IBM DDRS-39130D DC1B peripheral_type: disk [0x0] PROTECT=0 mode sense (10) cdb: 5a 00 01 00 00 00 00 00 fc 00 mode sense (10): pass-through requested 252 bytes but got 28 bytes Mode Sense (block descriptor) data, prior to changes: Number of blocks=17850000 [0x1105e90] Block size=512 [0x200] mode select (10) cdb: 55 11 00 00 00 00 00 00 1c 00 Resize operation seems to have been successful C:\sg3_utils-1.37>sg_readcap pd1 Read Capacity results: Last logical block address=891073 (0xd98c1), Number of blocks=891074 Logical block length=512 bytes Hence: Device size: 456229888 bytes, 435.095 MiB, 0.45623 GB Verifying that the SCSI hard drive with a capacity of 891074 blocks attached to the CMD CQD Q-Bus SCSI controller is seen as a drive with a capacity of 891072 blocks on VMS on a VAX CPU: $ MOUNT /FOREIGN BA215$DUA0: %MOUNT-I-MOUNTED, OVMSVAXSYS mounted on _BA215$DUA0: $ SHOW DEVICE /FULL BA215$DUA0: Disk BA215$DUA0:, device type RA81, is online, allocated, deallocate on dismount, mounted foreign, file-oriented device, shareable, available to cluster, error logging is enabled. Error count 0 Operations completed 4 Owner process "SYSTEM" Owner UIC [SYSTEM] Owner process ID 00000214 Dev Prot S:RWPL,O:RWPL,G:R,W Reference count 2 Default buffer size 512 Total blocks 891072 Sectors per track 217 Total cylinders 411 Tracks per cylinder 10 Volume label "OVMSVAXSYS" Relative volume number 0 Cluster size 0 Transaction count 1 Free blocks 0 Maximum files allowed 0 Extend quantity 0 Mount count 1 Mount status Process ACP process name "" Volume Status: Unknown ACP type. Verifying that the SCSI hard drive with a capacity of 891074 blocks attached to the CMD CQD Q-Bus SCSI controller is seen as a drive with a capacity of 891072 blocks on the 2.11BSD standalone disklabel on a PDP-11 CPU (ignore the "45Boot" which is a 2.11BSD bug that is fixed in a newer patch to correctly report "53Boot" on an 11/53 CPU). 9 8 7 6 5 4 3 2 1 Commands are Help, Boot, List, Map, Test and Wrap. Type a command then press the RETURN key: BOOT MU0 MU0 45Boot from tms(0,0,0) at 0174500 : tms(0,1) Boot: bootdev=06001 bootcsr=0174500 disklabel Disk? ra(0,0) 'ra(0,0)' is unlabeled or the label is corrupt. Proceed? [y/n] y d(isplay) D(efault) m(odify) w(rite) q(uit)? D d(isplay) D(efault) m(odify) w(rite) q(uit)? d type: MSCP disk: RA81 label: DEFAULT flags: bytes/sector: 512 sectors/track: 217 tracks/cylinder: 10 sectors/cylinder: 2170 cylinders: 410 rpm: 3600 drivedata: 0 0 0 0 0 1 partitions: # size offset fstype [fsize bsize] a: 891072 0 2.11BSD 1024 1024 # (Cyl. 0 - 410*) d(isplay) D(efault) m(odify) w(rite) q(uit)? q Label changed. Discard changes [y/n]? y 45Boot from tms(0,0,1) at 0174500 : Booting RSTS/E 10.1 from the SCSI hard drive with a capacity of 891074 blocks attached to the CMD CQD Q-Bus SCSI controller after the SIMH emulated RA81 disk image file with the RSTS/E 10.1 was dd to the SCSI hard drive: 9 8 7 6 5 4 3 2 1 Commands are Help, Boot, List, Map, Test and Wrap. Type a command then press the RETURN key: BOOT DU0 DU0 RSTS V10.1-L RSTS (DU0) INIT V10.1-0L Today's date? 20-FEB-19 Current time? 19:46 Start timesharing? <Yes> <stuff deleted> RSTS V10.1-L 20-Feb-19 07:46 PM User: 1,2 Password: Jobs detached under this account: Job What Size State Run-time RTS 1 ERRCPY 5K SR 13.6 ...RSX 3 OMS 9K SL 1.6 ...RSX 4 PBS... 19K SL 1.6 ...RSX Job number to attach to? Last interactive login on 20-Feb-19, 07:46 PM at KB0: Last non-interactive login on 20-Feb-19, 07:46 PM 3 other users are logged in under this account $ SHOW DISK Disk Structure: Dsk Open Size Free Clu Err Name Level Comments DU0 22 891072 837824 94% 16 0 RSTS10 1.2 Pub, DLW