BIOS boot partition, 4x3TB disks, and raid, problems with anaconda

[Chris Murphy]

On Aug 28, 2014, at 12:21 PM, Bruno Wolff III <bruno at wolff.to> wrote:
> 
> I think using raid 1 (with the 1.0 header format) can work well for that. There can still grub issues with having a boot just work, but at least you have the stuff you need available.

GRUB2 can locate vmlinuz/initramfs on md/mdadm raid0,1,10,5,6, even degraded. There is a BIOS specific limitation recognizing a certain number of drives. So you kinda have to watch out for that.

A possible problem with metadata format 0.9 (deprecated) and 1.0 is that the metadata is at the end of the partition; so in raid1 configurations, one of the partitions can be mounted normally as if there's no raid. The problem comes when modifying the volume, the raid metadata isn't updated. So when the raid is later assembled, md has no idea that one of the raid members is different than the other. This can quickly cause one or both members to become corrupted. So it's generally better (and recommended) to use metadata 1.2 format, which offsets the file system just beyond 4K from the start of the partition. That way a single raid member isn't mountable on its own, you have to first assemble the raid, then mount the file system.



Chris Murphy