[syslinux] syslinux, raid 1, and metadata 1.2

[Sven Köhler]

Hi,

it seems that booting from software raid 1 is not a problem, as long
you're using metadata version 0.9 or 1.0. Then, the raid metadata is at
the end of the device. But people found that there are certain risks,
for example that the filesystem can be mounted without using the raid
layer which may leave you with two copies that are out of sync.

Now metadata 1.0 and 1.2 put the metadata at the beginning of the
partition. While metadata 1.0 pretty much makes booting impossible,
metadata 1.2 should work just fine. There's 4 kilobyte of free space
at the beginning of the patition, before the metadata.

As far as I understand, the code in the MBR loads the VBR (boot sector
of the partition) and passes the number of the first sector of the
partition to the VBR. Usually, the VBR would be the code installed by
syslinux in the first sector of the filesystem. It loads ldlinux.sys I
believe?

With metadata 1.2, we can use the 4 kilobyte of free space to store a
small program that loads the first sector of the filesystem and
provides it with an "adjusted" sector number. That code would then run
normally and it would load ldlinux.sys as usual.

I found discussions of this, but they are from a long time ago.
Somebody said he even started coding. But it doesn't seem that the
latest syslinux supports booting from RAID 1 with metadata 1.2.
Nothing is written to the first 4 kilobytes of the RAID devices.

Was support for metadata 1.2 in the works? Has development stopped?


Kind Regards,
  Sven