Need help partitioning multiple disc drives
 

Hello everyone,

I have a problem that is driving me crazy. I'm trying to install a Debian system on a total of 4 9,1 GB SCSI-drives. My goal is to get all of these separate hard drives to work together as a combined disk space, prefferably in software-raid0. But this has proven to be quite hard to set up. I've managed to do this one time in the past, but i can't for the life of me figure out what I did differently. Anyway, I would really appreciate any help i might get on this issue.

Thanks alot!

Are you providing a non-raid0 location for /boot?

Due to grub limitations, /boot can’t be in a raid0. You should identically partition the drives to include some swap space and room for /boot, followed by the rest of each drive being either a single raid0 partition or divided up into several raid0 partitions as you see fit.

Regarding /boot, what I typically do with /boot on a multidisk setup is to place it into a raid1 with one or more spares. Grub works well with a raid1.

You can also set up what is called a scattered lvm instead of a raid0. A scattered lvm (really a scattered logical volume(s)) gives raid0 functionality without using mdadm.

All of this can be done using the Debian installer.


If my comments didn’t help, then post the specific problems you encountered.

So... have i interpreted this right if i where to configure each of my four disks like this (I've got 512 MB RAM)?:

25 MB | ext3 | /boot | Bootable flag on
256 MB Swap | bootable flag off
The rest as physical space for raid | bootable flag off

Then make a raid0-device, using the raid0-space as physical space for lvm and then creating a logical group and volume to hold the diskspace? Setting up the logical space as:

ext3 | / | bootable flag off ?

Is it possible to have multiple instances of /boot? :S Or did you take for granted that i would put them together into that raid1 thingie in the end?

BTW, a huge thank you for writing such a detailed answer to my question, i really appreciate it :)

Boot seems a little small, but like swap size, that’s one of the personal preference things.

And yes, you can have multiple partitions set up as /boot, say in a raid1, but grub will only looks in one of them (i.e., the one you define in grub as root). Of course, you need to properly define the location of /boot in menu.lst and fstab, which might be a raid1 or in a single partition.

You should only use an lvm if you are comfortable with managing one. A raid0 with an ext3 filesystem would work fine and would be simple to manage.

If you want to use an lvm, then you could either put it in a mdadm-based raid0 as you described or manually (before starting the installation) set up a volume group with the partitions instead of a raid0 and then define scattered logical volumes using the -i (--stripes) and -I (--stripesize) options during their creation. There is an example of this at the end of the lvcreate man page.

For reasons I don’t understand, the scattered lvm tends to be slightly faster than a raid0, and I mean almost trivially faster (maybe 2% on bulk reads/writes).

So you're saying i should put the root partition directly on a raid0-device? And do i have to scatter the boot and swap across the disks? Isn't it easier if i where to just use like 100 MB on one of the disks as /boot and another 1024 MB as swap (my amount of RAM doubled)? I'm very unskilled in this area of computer-operation and i hope i'm not making a complete fool out of myself, all I really want is an easy setup that let's me use the combined disk space.

Anyway, greatly appreciate you taking the time to answer