To "hardware" RAID 5 or software RAID 5

[Gordon Messmer]

Robin Laing wrote:
> 
> I was looking at 5 disks minimum in the new server.  The better recovery
> is what I am concerned with.  Just in case.  Backing up a TByte of data
> is a pain.

The probability of two simultaneous disk failures in an array that small 
are quite small.

> How hard to move from RAID 5 to RAID 6 using software RAID?

To the best of my knowledge, Linux doesn't offer RAID level migration. 
You'd have to back up your data, create a new RAID device, and restore.