[Techtalk] booting Linux software RAID

[Rudy L. Zijlstra]

Carla Schroder wrote:

>hu boy, here's another topic that inspires passions and debates. :) Any 
>thoughts on how to boot a RAID box? Here's the two main methods I've 
>collected so far:
>
>1. Put your root filesystem and boot directory or partition on a separate 
>disk, that is not part of the array. Such as a bootable CD, or an ATA hard 
>drive. Then start your RAID array (whether it's ATA, SATA, or SCSI) after 
>boot, via init.
>
>  
>
I am currently doing this. No huhu and works without problems. Will soon 
be doing it with yet a different machine with a RAID5 config on SATA.
Am also doing something similar on my main file server, though i am 
using HW SCSI RAID on that one.
Reason i don't boot from the HW raid is that most BIOSes can not handle 
booting from SCSI when an ATA disk is present.
I've got pretty bad experiences trying that. I use SCSI for regularly 
accessed data from several client machines, and ATA for seldom used mass 
storage like local distro mirrors.

>2. Put your root filesystem and bootdir/partition on the RAID disks, and 
>compile support into the kernel, to start it at boot time.
>
>This is for using Linux's software raid. Thoughts? Experiences? 
>
>  
>
Am thinking on adding that to my main file server. First action though 
will be to make *all* SCSI disks into mirror RAIDs.....
the one unmirrored disk failed and that failure has caused quit some 
problems:
- had to use a spare ATA disk while replacing the failed SCSI disk under 
warranty
- failure occured during backup, and this managed to trash the backup 
meta structure on the backup disk (@#$%).
   although the backup from that date is still readable, i can no longer 
add incrementals to it.

Limitation of that setup compared with HW RAID is that the bootblock is 
just on 1 disk, so failure of 1 disk will cause boot failure. HW mirror 
would solve that also.


Rudy