Bug#418519: Reason for having raw disk as physical volume
On Sat, Jan 03, 2015 at 09:48:14AM +0200, Vincas Dargis wrote:
> With HW Raid, it's exactly what we intended to do: create very small
> volume (for Linux point of view it's just /dev/sda) to be as "boot
> disk", containing only boot loader (and maybe /boot), which should
> not be ever resized or snapshoted or whatever, no need for LVM.
>
> Second volume (/dev/sdb) would be raw PV containing "/" and other
> LVM volumes. But I can't implement it simply by using partman.
I would think that having a partition on sda flagged bootable might
be necesary at least on systems. Many systems over the years have had
BIOS/firmware issues that insisted things had to look a certain way to
be bootable even if that wasn't officially a requirement. After all
that's how microsoft OSs were always installed, so making assumptions
was often considered valid since it always worked when tested.
So certainly not required, but might be safer.
Also there has to be somewhere to install the bootloader, and blockmapping
into the filesystem is a very bad idea, so having some space set aside
for the boot loader is a good idea (which often ends up being the unused
space of the disk before the 1st partition when doing 1MB alignment of
partition starts). With EFI you simply have a dedicated mandetory
partition to store the boot loader, but of course then you must also
have another partition for /boot in that case, since /boot has to be a
unix style filesystem, and the EFI boot partition has to be FAT (as far
as I know).
--
Len Sorensen
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