( sorrt for the delay in replying, I had a week off, and then a week catching up...) On Wednesday November 20, sdake@mvista.com wrote: > The only application where having a RAID volume shareable between two > hosts is useful is for a clustering filesystem (GFS comes to mind). > Since RAID is an important need for GFS (if a disk node fails, you > don't want ot loose the entire filesystem as you would on GFS) this > possibility may be worth exploring. > > Since GFS isn't GPL at this point and OpenGFS needs alot of work, I've > not spent the time looking at it. > > Neil have you thought about sharing an active volume between two hosts > and what sort of support would be needed in the superblock? > I think that the only way shared access could work is if different hosts controlled different slices of the device. The hosts would have to some-how negotiate and record who was managing which bit. It is quite appropriate that this information be stored on the raid array, and quite possibly in a superblock. But I think that this is a sufficiently major departure from how md/raid normally works that I would want it to go in a secondary superblock. There is 60K free at the end of each device on an MD array. Whoever was implementing this scheme could just have a flag in the main superblock to say "there is a secondary superblock" and then read the info about who owns what from somewhere in that extra 60K So in short, I think the metadata needed for this sort of thing is sufficiently large and sufficiently unknown that I wouldn't make any allowance for it in the primary superblock. Does that sound reasonable? NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
