On Wed, May 16, 2012 at 6:38 PM, NeilBrown <neilb@xxxxxxx> wrote: > On Thu, 17 May 2012 03:24:26 +0200 Oliver Martin <oliver@xxxxxxxxxxxxxxxx> > wrote: > >> Hi, >> >> is there any specific reason why md refuses to create a RAID6 array with >> 3 disks? My (probably naive) understanding suggests it should be the >> same as a 3-disk RAID1, similar to a 2-disk RAID5. > > I'll have to leave for for hpa to answer. I've occasionally thought that > maybe it should be fixed, but it never seemed worth the effort. The math assumes 2 data disks. >> The reason I'm asking is that I currently have space on three disks for >> a new array, and would like to expand it when I add a fourth. I tried >> this scenario with a few loopback devices, but the only way to go from a >> 3-disk RAID1 to a 4-disk RAID6 seems to be via an intermediate 3-disk >> RAID5, requiring two reshapes. I'd like to avoid one of them, if at all >> possible. > > Yes, not possible at present. > It might be as simple and finding the places that impose the limit and delete > them... You'd certainly need to route around the acceleration code, because that increased the dependency on the assumption that there is always two data disk slots. -- Dan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
