Re: Workarounds for advanced RAID features in GRUB Legacy?

[Leif W]

> From: "Tim Woodall" <address@hidden>
> Sent: 2005 September 10 Saturday 17:02
>
> > On Sat, 10 Sep 2005, Leif W wrote:
> >
> > Specific areas:
> >
> > * RAID 1, RAID 10, RAID5
> > * Partitionable RAID devices
> > * Picking the most up-to-date drive
> >
> > Right now the cleanest option seems to be to simply put a separate 
> > ext2 partition at the beginning of each disc, have a kernel and 
> > initrd there to handle the RAID setup, and install grub multiple 
> > times, and update everything manually.  But I have SATA discs, which 
> > are treated like SCSI discs, and thus
>
> What I've got is a raid1 /boot (md0) ext3 at the start of the disk and
> then the rest of the disk is md1 which is then partitioned using LVM2.
> (I'm just using raid1 on two IDE disks here)

Well, even here, let's take a closer look.  An ext3, is that including a 
separate partition for a journal device?  And a swap partition?  You 
don't want to mirrow swap, and no need to make it RAID 0, as Linux swap 
is designed to balance the disc utilization.  So we have journal, boot 
(RAID 1), swap, and data (root, RAID 1).  That's 4 partitions already. 
I've got discs that are huge, and can easily fit several OS 
installations, and need to have some, all on the same discs.  But the 
SATA discs have 16 partition limit that I bump into if everything is a 
flat level RAID 1.  That's my dilemma.  With WinXP, it requires the DOS 
partition table, and is very picky about partition types for a clean 
install.  And is further picky about partitions changing later.  And 
can't handle SW-RAID for a single partition, only the full disc, only 
using the BIOS RAID.

> And then my menu.lst looks something like this:

> <snip>

> You still need to install grub into the boot sector on both disks but
> once that is done then any updates will update both drives (except for
> updating the boot sector or partition table)
>
> If either drive fails then the system will boot from the other one 
> (you
> might need to unplug the failed disk to make the bios happy)

This looks similar to some other configs that I've seen and I'll try 
this technique as well.  The other technique I saw suggested using the 
'device' command to assign subsequent discs to hd0.  The thing is, I 
don't want to have to pull out plugs.  I mean, if something fails, 
granted I need to power down and pull out plugs and swap the drives. 
But maybe I don't have time at the moment, and just need to limp along 
until I have sufficient time to obtain a disc (save money, purchase, 
have it delivered, test it before using, and so on).  But bills need to 
be paid, data needs to be accessed.  I may not want to fiddle with my 
drives until I have the replacement parts.  Or the other situation, 
maybe everything is fine, but I goof up a config file.  I don't want to 
have to be pulling plugs to get back in.  I don't want to cause excess 
wear on my plugs.  :-D  So, a solution I'm hoping to find will just 
either try the next device/disc/partition/raid in a list, or I'll just 
settle for hitting a down arrow to go to the next menu item.

> All of this is done using stock debian (sarge).
>
> I've considered playing with making the entire disk raid1, including 
> the
> boot sector and partition table but I've never got around to it and 
> I'm
> not certain it can be made to work (easily).

Yeah I've been looking at this.  Boot on RAID1.  It's fairly well 
described in the Software RAID HOWTO, but there are some gaps missing, 
like anything.  And the GRUB specific config isn't too in-depth.  For me 
personally, it just feels like ugly workarounds, not some very elegant 
solutions.  So now I'm considering the initrd on boot partition method, 
but might need loopback support and nice to have CramFS support, but 
ext2 might suffice.


Thanks again for all the ideas!  I'm going to try as much as I can this 
weekend.


Leif