Re: Support of advanced RAID features in GRUB 2?

[Leif W]

> From: "Marco Gerards" <address@hidden>
> Sent: 2005 September 10 Saturday 14:11
>
> "Leif W" <address@hidden> writes:
>
> Hi,
>
> > There seem to be some areas where support hasn't been implemented in
> > GRUB 2.  I've checked the manual, FAQ and the archives of this
> > list. Firstly I was wondering if there were any known workarounds 
> > with
> > GRUB 2, from the ugly or tedious to the not-so-bad techniques, any 
> > and
> > all. Secondly I was just wondering if anyone had any plans for this?
>
> You are right, GRUB 2 is still in development and missing many
> features.

Right, but the other part of the question had to do with some planning. 
I did see a TODO page in the Wiki, but not much indication of status, as 
in "it would be nice to do" (requirements gathering), "I've been 
thinking of how to do" (design), or "I was planning to do it" 
(implementation), or "it's in CVS now" (testing).  Just curious about a 
rough idea of what stage these things are at right now.

> > * RAID 1, RAID 10, RAID5
>
> What kind of support would you like for RAID 1?  It's a mirror so it
> should work now, right?

Well, normally, but there's the cases when it's not an exact mirror. 
Say I changed some files and one disc wrote but there was a power outage 
before the other finished, or the disc failed mid-write so only one disc 
could be written.  Or everything seems to be working fine, but one day I 
go to boot up and one disc is bad.

> How should GRUB detect RAID devices?  Or should the user configure it
> manually?

Well, there's two parts to the question, from a user view and a 
programmer view.  As a user, I'm asking about the existing configuration 
options.  How might I achieve the desired ends?  The other half for 
programmers might be to ask, "How would I inspect a disc and determine 
if it's a RAID device, and how to proceed?"  I do not know enough about 
the specific format of the partition tables, raid super blocks or 
filesystem super blocks, or how to integrate with existing code 
libraries to make these data structures more easily digestible.  I can 
only speculate.  Right now, I'd settle for even specifying manually in 
GRUB on each boot, and write the working config to a file and generate a 
GRUB boot floppy while I work out the rest of the specifics.

> > * Picking the most up-to-date drive
>
> Can you please explain this in detail?

See above.

One of my questions was missing, that of partitioned RAID arrays. 
Another question I tacked on to a subsequent email, that of how to 
handle LVM on top of RAID.  I'm just skimming through various config 
options in Linux Software HOWTO, where it mentions a benefit of putting 
LVM/EVM on top of raid is partitions can be non-destructively resized, 
and some file systems like XFS support non-destructive hot resizing 
(I.E. for root).  No rebooting to a Knoppix disc, backing up data, 
fiddling with partition sizes and limitations, restoring data.  But 
then, I don't have any idea if XFS is supported by GRUB either.  :-)

With all of these more more complex or esoteric configurations, it is 
looking more and more like the only generic solution is to use an 
initial ram disc with kernel, and ram disc placed on a very conservative 
partition and file system, possibly at the beginning of the disc (if it 
might move onto older hardware with a 1024 cylinder boot limitation).

Leif