Bootable Linux RAID

[time]

Is there a way to mirror an existing Linux bootable partition/drive? The techniques I've seen on the net seem to assume you have a third partition/drive available.

It looks like Suse YAST should be able to do it - you can remove the / mountpoint and create the RAID, but it fails when you try to apply all this.

I've edited the raidtab file and all looks okay. Makeraid chokes because / is still mounted. I figure I can't umount it while I'm running ...

Is mdadm or some other utility any help here?

I'm also wondering about GRUB support for bootable software RAID. What I've read suggests only LILO is compatible, but AFAIK Suse uses GRUB by default.

It's easy enough if you have a separate boot drive, but I'm lost in this situation. While I'm at it, does anyone recommend a particular partitioning layout? I'm just using one (+ swap).

 

[blakerwry]

you're not going to be able to do anything with / mounted.

I'd suggest booting from knoppix, creating an array and them moving the data over to the array... this would require 3 partitions or at least an image stored somewhere + 2 partitions for the array.

dd might give the cleanest move... dont forget to edit your etc/fstab to point to the correct md device...

also, if you're booting from the array you'll want to follow some guide on making a linux RAID array bootable (http://www.faqs.org/docs/Linux-mini/Boot+Root+Raid+LILO.html#toc3)


personally, I'd ditch the idea... you're probably better off without the RAID and just keep a good backup/image of the drive.

 

[time]

personally, I'd ditch the idea... you're probably better off without the RAID and just keep a good backup/image of the drive.

Sh*t! Anyone can do this standing on their head in Windows; you're telling me that bootable software RAID under Linux is nothing but grief? Good grief!

Unfortunately, things have taken a turn for the worse. Something I tried (don't know what) left me with a GRUB prompt - and no obvious way to complete a boot, Linux or Windows.

Despite trying various repairs etc, I wasn't able to shift it. I tried to convert to LiLo but it didn't seem to fully take (and this is Suse 9.2!). I also tried to mirror the partitions and mount them with LiLo. I ended up with a boot process that says "GRUB" ... and that's it.

At this point, I resorted to fdisk /mbr. Now, I have ABSOLUTELY NOTHING!

Tomorrow, I will completely erase partition information (on both drives) and try again. At the moment, my confidence in Suse/Linux/Open Source is at about one out of ten.

Blakerwry, I value your advice very highly indeed. I NEED mirrored drives here, and I don't have access to cheap 3Ware controllers. ANY suggestions from anyone will be gratefully received.

 

[CougTek]

Unfortunately, things have taken a turn for the worse. Something I tried (don't know what) left me with a GRUB prompt - and no obvious way to complete a boot, Linux or Windows.

Let me guess : You've installed GRUB on your Linux partition and then blew up your Linux partition. I did that a few times...

 

[blakerwry]

I was under the impression that windows wouldn't boot from a software array either... maybe that is just RAID 5/0 that wont boot.


If you're interested in a 3ware controller I have one I could sell you. It's an older 5400 controller and does not support the online or CLI manaement, it is also slow... but it will get you hardware RAID1. $30 sounds right or you can hunt ebay for something newer. I've purchased 6200 cards for ~$30 and 7500-4 cards for ~$150.

 

[time]

The nVidia RAID utility for Windows handles everything we've talked about easily; you can definitely boot from the array. Apparently, it can even convert from one type of RAID to another.

My problem goes much deeper than I thought. Foolishly, I believed the 'gurus' who claimed that nVidia RAID was "fake" or software RAID. In fact, for nForce 4 at least, it's at least partially hardware based ('accelerated').

I have no idea how I got Suse working at all on this platform, but I certainly can't repeat it. With a BIOS array configured, DOS and my partition utilities see the array as a single drive. Linux, of course, likes to ignore the BIOS and sees it as two separate drives. However, all efforts to control the boot sector failed (after appearing to work). But as soon as I unmirror the drives, GRUB happily kicks in. :-?

Suse 9.0 (32-bit) can't see either the array or the individual drives. Suse 9.2 sees individual drives but partially acts as if it's dealing with an array.

This sucks. I'm now in the bleeding edge position that I loath and detest. :x I'm on a deadline to ship this server and I can't even mirror the disks.

 

[blakerwry]

As far as I am aware, the Nvidia RAID is equivalent to an intel, promise, or highpoint host based RAID, meaning they use drivers to accomplish their RAID functions. You wont be able to use them in linux without the special drivers, which may or may not exist. (usually the latter)

If this is a linux server, then I would strongly suggest hardware RAID.

 

[blakerwry]

If you're really in a pinch I could sell you a 3ware 6200-2, good for RAID 0/1 in linux and works with the CLI and web based management for $40+s/h.

I was going to use it in a server I'm building, but I think you need it more.

 

[time]

Thanks for the offer, Blake, but I need a solution by tomorrow - I'm a little far away for an overnight delivery.

I think I've got software RAID working with a separate boot partition. Extremely clunky, but it might have to do.

 

[time]

For completeness, I ended up creating a two cylinder (16MB) boot partition and installing GRUB in that. It was the only way I could get it all to hang together. Mirroring the boot partition causes the boot process to fail, so I have to fudge around to ensure the second drive can boot independently. Not a good situation when a technician with no Linux knowledge has to replace one of the drives.

From what I've read, I suspect Suse 9.2 Pro just doesn't properly support bootable software RAID. FC3 is worse. The enterprise editions apparently do, which I think is rather pointless. For example, the utility that automatically partitions, formats and remirrors a replacement drive is only included with Suse Enterprise.

I have to say that I've lost an awful lot of confidence in YAST. It was causing a lot of my pain. I'll also blame nVidia for not providing a Linux driver for their RAID controller, but most of all, I'm stunned by the poor and inconsistent design in Linux distros when it comes to something that Novell could manage twenty years ago.