Bill Davidsen <davidsen@xxxxxxx> writes: > Goswin von Brederlow wrote: >> Hi, >> >> consider the following situation: You have a software raid that runs >> fine but one disk is suspect (e.g. SMART says failure imminent or >> something). How do you replace that disk? >> >> Currently you have do fail/remove the disk from the raid, add a >> fresh disk and resync. That leaves a large window in which redundancy >> is compromised. With current disk sizes that can be days. >> >> It would be nice if one could tell the kernel to replace a disk in a >> raid set with a spare without the need to degrade the raid. >> >> Thoughts? >> > > This is one of many things proposed occasionally here, no real > objection, sometimes loud support, but no one actually *does* the code. > > You have described the problem exactly, and the solution is still to > do it manually. But you don't need to fail the drive long term, if you > can stop the array for a few moments. You stop the array, remove the > suspect drive, create a raid1 of the suspect drive marked write-mostly > and the new spare, then add the raid1 in place of the suspect > drive. For any chunks present on the new drive the reads will go > there, reducing access, while data is copied from the old to the new > in resync, and writes still go to the old suspect drive so if the new > drive fails you are no worse off. When the raid1 is clean you stop the > main array and back the suspect drive out. > > This is complicated enough that I totally agree a hot migrate would be > desirable. This is why people use lvm, although I make zero claims > that this same problem will solve more easily, I'm just not an lvm > guru (or even a newbie, just an occasional user). The difference, appart from simpler usage, would be that the raid does not have to be stoped. Stopping the raid that contains / or /usr means some downtime. In the case of LVM there is the fact that you can suspend a device-mapper device and alter its mapping any way you wish. So you can do things manually without umounting the filesystems. But lvm / device-mapper doesn't have all the raid stuff so one can't just switch. -- 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
