On Mon, 10 Sep 2012 16:43:14 +0000 Ming Lei <Ming.Lei@xxxxxxxxxxxx> wrote: > Neil, > > How about the other scenario: I plug out a drive and put aside for a while and put it back to the same machine with bitmap enabled for the raid6 array? Does it do full-recovery or fast resync? If the array has been degraded that whole time, it will do a fast resync. > > I noticed either md superblock or bitmap superblock has events recorded and I guess it may be used to identify the up-to-date drive or the old drive put back again. Correct. NeilBrown > > Thanks > Ming > > -----Original Message----- > From: NeilBrown [mailto:neilb@xxxxxxx] > Sent: Sunday, September 09, 2012 3:51 PM > To: Ming Lei > Subject: Re: question about bitmap for raid6 > > On Sat, 8 Sep 2012 21:07:46 +0000 Ming Lei <Ming.Lei@xxxxxxxxxxxx> wrote: > > > Hi Neil, > > > > We use 2.6.32 in house and most recently we found something bad happen when we turn on bitmap for raid6 array. Let me ask a question to help me to understand our situation. > > > > Say I have two hardware identical PCs(name them A and B) running with the same linux distribution. Both box has an raid6 array assmeblying 7 drives with internal bitmap. If I yank out one drive from PC B to make this drive slot empty, and then yank out a drive from PC A and move it to PC B, would md driver force the raid6 array on PC B rebuild(take a long time) or just do resync(very short time)? What's the condition on bitmap code to check if it is really the drive I just pull out from the same machine or it is the drive pulled out from different machine? > > > > Thanks > > Ming > > PC B would not do anything to drive that you moved from PC A until you add it as a spare. Then it will perform a complete rebuild of the missing device to the new device. It will not do a partial recovery. > > 'md' knows it is a device from a different array because the 'uuid' stored in the metadata is different. > If you managed to create two arrays on two different PCs which both had the same UUID, then you could definitely get strange data corruption happening, but that is very unlikely. > > NeilBrown > > -- > 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
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