On 6/9/2013 5:47 AM, Roman Mamedov wrote: > On Sat, 8 Jun 2013 20:18:10 +0200 > Ramon Hofer <ramonhofer@xxxxxxxxxx> wrote: > >> My home server with a linear raid (md0) containing three raid5 (md1, >> md2, md3) is still working wonderfully. Thanks again Stan! >> >> Now I'm planning to add a fourth raid5 to the linear array. > > You should have used LVM instead of md linear to join your RAIDs into a single > block device. LVM allows placing a single logical volume over physical extents > placed in all sorts of non-contiguous, fragmented, overlapping fashions. You > could also transparently migrate portions of those physical extents between > physical arrays without even having to unmount the filesystem that you have on > the LV. FYI, I designed this architecture for Ramon. He CC's linux-raid as a courtesy so that others may learn from his experience with it, and in the event I may be unavailable. Yes, LVM could have been used. It was specifically not used because Ramon is using XFS, which is stripe aligned to each constituent RAID5 array, which each contain a fixed set of allocation groups. I'm sure you understand the negative performance implications involved when breaking alignment with parity RAID, or moving parts of an AG from one disk or array to another. -- Stan -- 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
