RE: Does GRUB2 support software raid?

[Jake Thomas]

Hi Da-Shi!

      That was mind-expanding! I didn't know Grub supported RAIDing two 
partitions together. I thought you were supposed to only be able to RAID whole 
hard drives together with Grub (but the RAID module crashes Grub, preventing 
success in this endeavor), though I knew that once in Linux, all kinds of crazy 
things could be done with LVM, mdadm, and who knows what all else. Heck, it 
could probably RAID a whole hard drive with a partition, lol.

   I certainly like this idea of RAIDing partitions rather than whole hard 
drives. That puts Grub code outside any RAIDing, allowing the BIOS to load Grub 
without "software" RAID support. You could even have each hard drive have a 
BIOS boot partition not a part of any RAID, and also have each hard drive have 
a partition for RAIDing. RAIDing partitions sounds like less of a potential 
disaster than RAIDing whole drives.

  When you said you are going to experiment with spanning the entire hard 
drives with one partition, you didn't mean that literally, right? If you did, 
there would be no room for Grub unless you used a block list. Spanning a hard 
drive with one partition without a partition table or MBR or anything is called 
a "superfloppy". You literally format /dev/sdX[no number here] to a filesystem. 
The whole hard drive is just a partition.

    Are you sure the BIOS can see the virtual fake RAID drive? If you press F12 
or del (or whatever it is you press for your particular BIOS to see available 
bootable drives), does the virtual fake RAID drive show as an option? If it 
doesn't the BIOS can't boot such a thing. But if you only RAID partitions 
instead of whole hard drives, then Grub is outside any RAIDing, and the BIOS 
just boots one of the physical hard drives.

   Did you delete the partition tables of /dev/sda and /dev/sdb before creating 
/dev/md0?

    And, out of curiosity, how is Grub recognizing that the two partitions are 
RAIDed together? Do they haves special partition type IDs that show that the 
partitions are for RAIDing? Even if that was the case, how does it know which 
partition to RAID with what?

Regards,
Jake

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