how does GRUB read from /boot on software-RAID partition?




Some articles about GRUB and md-based RAID1 (mirroring) seem to imply that GRUB
can read files (including the kernel and the initrd file) from /boot on the
filesystem on a mirrored partition.

Since GRUB hasn't loaded the kernel file yet, GRUB can't be using the kernel
and its md driver, and therefore can't be reading the partition _as_a_RAID_
_volume_ (/dev/mdX), right?


So is GRUB just reading the partition directly to get to the file system?

Specifically, is GRUB taking advantage of the fact that the RAID metadata is
written at the end of a partition that is a component of a RAID volume (and
that a file system doesn't care if the block device it's in actually contains
more blocks than the filesystem knows about)?


If so, how reliable is that?

Should one put /boot on a plain, non-RAID partition on one disk and somehow
(manually or automatically) maintain a backup /boot partition on the second
disk, or is it fine to put /boot on a mirrored partition (so maintaining
redundancy is automatic) and let GRUB read the partition directly?


Thanks,
Daniel
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