Software RAID and a bootable cd-rom

[ds123]

I am going to be setting up a new system and I am going to use software RAID.

I see in the guidelines that it is recommended that the boot drive not be part of the raid system. It pains my thrifty nature to use a several GB drive for just booting the system, since the boot partition is typically so small.

Is there any reason why I couldn't just set up a cd-rom as the boot drive to act as the boot partition? Is this a dumb idea, and if so why?

I assume that it is problematical to set up grub on the cd, and so I need to research what is needed for an ISO for the cd. Can anyone point me in the right direction?
Edit: it doesn't look bad, here are some directions: http://www.gnu.org/software/grub/manual ... D-ROM.html

In the documentation it says:

Note: It is not recommended to put the following directories in an LVM2 partition: /etc, /lib, /mnt, /proc, /sbin, /dev, and /root. This way, you would still be able to log into your system (crippled, but still somewhat usable, as root) if something goes terribly wrong.

This advice seems to eliminate many of the benefits of having a RAID system. This doesn't seem like advice that I would want to follow, because if I was in a real jam, I would just boot off a Gentoo Installation cd as if I was going to set up the system again. It makes it seem like software RAID is kind of risky, since all your /etc/ settings would not be part of RAID. What are your thoughts on that?

Thanks for any help you can give me.

[NeddySeagoon]

ds123,

With kernel raid, you can make boot either unraided or raid1. I use raid1 in my setup.

I have 4 drives all partitioned like this:-

Code: Select all

  Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1           5       40131   fd  Linux raid autodetect
/dev/sda2               6          70      522112+  82  Linux swap / Solaris
/dev/sda4              71      121601   976197757+   5  Extended
/dev/sda5              71         724     5253223+  fd  Linux raid autodetect
/dev/sda6             725      121601   970944471   fd  Linux raid autodetect

Where /dev/sd[abcd]1 is boot in raid1
/dev/sd[abcd]2 is four equal priority swaps - the kernel manages them
/dev/sd[abcd]5 is raid5 root, outside lvm, so I don't need an initrd to start lvm to get at root
/dev/sd[abcd]6 is raid5 lvm for everything else.

[ds123]

Thanks very much for your reply.

I've been mulling over what you have written and have realized some additional questions and comments:

1. I was originally under the impression that raid1 meant only using two drives, studying your diagram and reading a little helped me to understand that two drives was a minimum not a maximum. Thank you.

2. In your partitioning scheme, if I understand it, you are saying that the swap space is not covered by RAID. Suppose that one of the drives fails and the kernel is in the process of attempting to use swap info on the failed drive. What happens?

3. I hadn't thought about the separation of lvm and root, so thank you for that.

[NeddySeagoon]

ds123,

When you lose swap, the application that has lost its data dies a horrible death.

I could raid5 the swaps but they are close enough to the front of the drive so I can steal on to do a native install of DOS or Windows 3.1, just for old times sake.
Even then, I could fail onr of the partitions in the raid and allow swap to operate in degraded mode.

[ds123]

Thanks for your help.