Hello!
> The OpenBSD installer partitioning does not accept more than 15
partitions
> with GPT (partitions 'c' and 'i' are already defined in advance by the
> installer). It limits from partition 'a' to 'p', but GPT partitions must
> support up to 128 partitions.
It is actually more restricted:
- yes, total amount of disklabel slices is 16 - 'a' to 'p'
BUT:
- only first 8 slices are reserved for OpenBSD slices inside single GPT
partition with OpenBSD ID. Where 'b' is reserved for swap, and 'c' is
always whole disk. So only 6 slices are available for slices inside
OpenBSD partition
- another 8 slices are automatically used to map other GPT partitions.
So you can access from OpenBSD up to 8 others partitions in GPT.
Later mechanism is done by function spoofgpt() in
/usr/src/sys/kern/subr_disk.c - see
https://cvsweb.openbsd.org/src/sys/kern/subr_disk.c?rev=1.272&content-type=text/x-cvsweb-markup
To fully understand it, here is complex example of my GPT disk
partitioning (note that I actually use BIOS mode, which is not
officially supported on OpenBSD, but it works fine using Linux + GRUB to
load OpenBSD kernel).
GPT partitions as seen by OpenBSD fdisk:
isk: sd0 Usable LBA: 34 to 937703054 [937703088 Sectors]
#: type [ start: size ]
------------------------------------------------------------------------
0: BIOS Boot [ 34: 2014 ]
1: EFI Sys [ 2048: 2097152 ]
2: Linux LVM [ 2099200: 312473601 ]
3: EFI Sys [ 314574848: 204800 ]
4: OpenBSD [ 314779648: 102400000 ]
5: NetBSD [ 417181696: 100663296 ]
6: 49f48d32-b10e-11dc-b99b-0019d1879648 [ 517844992: 16777216 ]
7: 83bd6b9d-7f41-11dc-be0b-001560b84f0f [ 534622208: 1024 ]
8: 516e7cb6-6ecf-11d6-8ff8-00022d09712b [ 534623232: 104856576 ]
9: 516e7cb5-6ecf-11d6-8ff8-00022d09712b [ 639479808: 16777216 ]
10: Linux files* [ 656257024: 104857600 ]
And here is disklabel (omitted header):
16 partitions:
# size offset fstype [fsize bsize cpg]
a: 98205696 314779648 4.2BSD 2048 16384 12960 # /
b: 4194304 412985344 swap # none
c: 937703088 0 unused
i: 2014 34 boot
j: 2097152 2048 MSDOS
k: 312473601 2099200 unknown
l: 204800 314574848 MSDOS
m: 100663296 417181696 unknown
n: 16777216 517844992 unknown
o: 1024 534622208 unknown
p: 104856576 534623232 unknown
Note that:
- slices 'a' to 'h' are usable for OpenBSD, however 'a' should be root
filesystem, 'b' should be swap, and 'c' is synthetic entry covering
whole disk. All these slices are always inside single GPT partition of
type OpenBSD - in this case: 4: OpenBSD
- slices from 'i' to 'p' are automatically mapped other GPT partitions.
You can see (matching offset), that
- slice 'i' is GPT partition 0: BIOS Boot
- ... slice 'p': is GPT partition: 8: 516e7cb6-6ecf-11d6-8ff8-00022d09712b
- however it means that additional GPT partitions (starting from 9) are
simply NOT accessible from OpenBSD.
So briefly:
- there are total 16 slices ('a' to 'p') available
- first 8 slices are used to map OpenBSD slices inside single OpenBSD
GPT partition (but 'a', 'b', 'c' have special meaning as described above)
- remaining 8 slices are automatically mapped remaining GPT partitions
so they can be accessed from OpenBSD (through device in /dev/)
Hopefully it will make things more clear.
Best regards
--Henryk Paluch
On 12/18/23 17:15, spnti wrote:
Hello guys!
The OpenBSD installer partitioning does not accept more than 15 partitions
with GPT (partitions 'c' and 'i' are already defined in advance by the
installer). It limits from partition 'a' to 'p', but GPT partitions must
support up to 128 partitions.
Thank you for your attention and help.
