> I read the sun manpage for format, but it is pretty terse,
> and doesn't give me much guidance regarding partitioning new volumes.

True.

I do it like this under SunOS4. Be careful to choose the correct disk.
The usual comment about backups can be repeated here. Comments 

>>>> LIKE THIS 

in the text below are mine. Enjoy...

# format
Searching for disks...done


AVAILABLE DISK SELECTIONS:
        0. sd1 at esp0 slave 8
           sd1: <ST4702N cyl 1544 alt 0 hd 15 sec 50>
        1. id000 at idc0 slave 0
           id000: <Seagate IPI ZBR Elite cyl 1893 alt 1 hd 17 sec 78>
Specify disk (enter its number): 0
selecting sd1: <ST4702N>
[disk formatted, defect list found]


FORMAT MENU:
        disk       - select a disk
        type       - select (define) a disk type
        partition  - select (define) a partition table
        current    - describe the current disk
        format     - format and analyze the disk
        repair     - repair a defective sector
        show       - translate a disk address
        label      - write label to the disk
        analyze    - surface analysis
        defect     - defect list management
        backup     - search for backup labels
        quit
format> part


PARTITION MENU:
        a      - change `a' partition
        b      - change `b' partition
        c      - change `c' partition
        d      - change `d' partition
        e      - change `e' partition
        f      - change `f' partition
        g      - change `g' partition
        h      - change `h' partition
        select - select a predefined table
        name   - name the current table
        print  - display the current table
        label  - write partition map and label to the disk
        quit
partition> a

        partition a - starting cyl      0, # blocks    75000 (100/0/0)

Enter new starting cyl [0]: 
Enter new # blocks [75000, 100/0/0]: 40000
partition> pr
Current partition table (unnamed):
        partition a - starting cyl      0, # blocks    40000 (53/5/0)
        partition b - starting cyl    100, # blocks   375000 (500/0/0)
        partition c - starting cyl      0, # blocks  1158000 (1544/0/0)
        partition d - starting cyl      0, # blocks  1158000 (1544/0/0)
        partition e - starting cyl      0, # blocks        0 (0/0/0)
        partition f - starting cyl      0, # blocks        0 (0/0/0)
        partition g - starting cyl    600, # blocks   525000 (700/0/0)
        partition h - starting cyl   1300, # blocks   183000 (244/0/0)

>>>> OK, NOW LET'S ADJUST TO CYLINDER BOUNDARY 

partition> a

        partition a - starting cyl      0, # blocks    40000 (53/5/0)

Enter new starting cyl [0]: 
Enter new # blocks [40000, 53/5/0]: 60/0/0

partition> b

        partition b - starting cyl      0, # blocks       0 (0/0/0)

Enter new starting cyl [0]: 60

>>>> CONTINUE IN THE SAME MANNER FOR ALL PARTITIONS. TRADITIONS SAY TO USE
>>>> g FOR /usr AND c IS AS USUAL THE WHOLE DISK. THE MATHEMATICS ARE THAT
>>>> START(a) = 0
>>>> START(c) = 0
>>>> START(a) + SIZE(a) = START(b)
>>>> START(b) + SIZE(b) = START(g)
>>>> START(g) + SIZE(g) = SIZE(c)
>>>> USE ONLY WHOLE CYLINDER BOUNDARIES (LIKE 60/0/0)
>>>> THERE ARE NO WARNINGS FOR OVERLAPPING PARTITIONS

>>>> FINALLY (MAKES CHOICES PERMANENT):

partition> la
Ready to label disk, continue? y

partition> q
format> q
#

Harald.