Convert existing software Raid 1 to Raid 10?

[ghettodev]

I've been playing around with raid last week or so and cant seem to find the right config to get a raid 1 /boot and a raid 10 at / working. It seems that in principal it should be easy enough.

I have 4 disks. /boot is raid 1'ed across all four, I'm using 2 drives in a raid 1 array for / and I've created another empty array of 2 drives in raid 1 with same size and geometry. I thought I could simply boot into the live cd, create a new raid 0 array of /dev/md1 and /dev/md2 to create a raid 0 /dev/md3, update fstab and grub and reboot. No such luck though. Grub wont boot from it and attempting to mount it from the live cd tells me wrong mount point, bad fs or no superblock.

Anyone know if I can add an empty raid one array to an existing raid one array and turn it into a raid ten "/"?

[fangorn]

AFAIK the only way such "conversion" is working is if you create a RAID 1 of two RAID0 systems of exact same geometry and setting the copy part dirty and reinitializing it.

If your RAIDs are still empty I would start from scratch and setup a RAID 0 over hda/hdc which you mirror with RAID1 on a RAID0 on hdb/hdd (insert your actual drives and partition numbers yourself). This is the classic RAID10 configuration.

[ghettodev]

I was wondering about that, I've read that grub wont boot from a raid 0 but I was assuming that meant the /boot partition, are you saying that grub cant read raid 0 on any partition?

[fangorn]

AFAIK grub cannot read any raid. Grub is able to boot from RAID 1 because the information ist stored in the same proper order on all used partitions. Grub for this accesses one single partition as this, not as part of a raid. All other RAID version do not use the partition logic so grub cant see the data on them.

But grub only has to read the /boot partition, the rest of the starting process is left to the kernel, so any system readable by the kernel is possible.