Alan Mackenzie:
> On Fri, Dec 20, 2024 at 15:50:53 +0100, k...@aspodata.se wrote:
...
> Because I didn't know about it. I found out about it this morning, and
> immediately tested it by setting up an
> "md=126,/dev/nvme0n1p4,/dev/nvme1n1p4" on the kernel command line, using
> the rescue disk to make the "preferred minor"s wrong, and testing it.
> It worked!
>
> If I understand things correctly, with this mechanism one can have the
> kernel assemble the RAID arrays at boot up time with a modern metadata,
> but still without needing the initramfs. My arrays are still at
> metadata 0.90.
Please tell if you make booting with metadata 1.2 work.
I havn't tested that.
///
...
> > And... what is the need for dynamic minors now when dev_t is 32bits:
> Dynamic minors? I don't think I follow you, here.
If you partition the md device, the partitions will get a device with a
dynamic minor.
# mdadm -C /dev/md11 -n 1 -l 1 --force /dev/sdc2
# mdadm -C /dev/md10 -n 1 -l 1 -e 0 --force /dev/sdc1
... create partitions
# fdisk -l /dev/md10
...
Device Boot Start End Sectors Size Id Type
/dev/md10p1 2048 22527 20480 10M 83 Linux
/dev/md10p2 22528 192383 169856 82.9M 83 Linux
# fdisk -l /dev/md11
...
Device Boot Start End Sectors Size Id Type
/dev/md11p1 2048 206847 204800 100M 83 Linux
/dev/md11p2 206848 1757183 1550336 757M 83 Linux
# cat /sys/block/md10/md10p1/dev
259:0
# cat /sys/block/md10/md10p2/dev
259:1
# cat /sys/block/md11/md11p1/dev
259:2
# cat /sys/block/md11/md11p2/dev
259:3
$ grep -A2 '259 block'
/Net/git/linux-stable/Documentation/admin-guide/devices.txt
259 block Block Extended Major
Used dynamically to hold additional partition minor
numbers and allow large numbers of partitions per device
So, to boot to a md device partition (as /) might be a hit and miss
unless you use some initramfs magic.
Regards,
/Karl Hammar
