On Tue, 10 May 2011 21:04:29 -0400 Dylan Distasio <interzone@xxxxxxxxx> wrote: > It's possible I did use different versions but I thought I had > upgraded both of them right before the reshapes. Sorry if this is an > elementary question, but does writing the 2nd parity block always to > the last drive instead of rotating it increase the odds of a total > loss of the array since the one specific drive always has the 2nd > parity block? No. The only possibly impact is a performance impact, and even that would be hard to quantify. The reason that parity is rotated is to avoid a 'hot disk'. Every update has to write the parity block and if they are all on one disk then every write will generate a write to that one disk. Because of the way md implements RAID6, every write involves either a read or a write to every device, so there is no real saving in rotating parity. I think (but am open to being corrected) that rotating parity is only important for RAID6 if the code implements 'subtraction' as well as 'addition' for the Q syndrome (which md doesn't) and if you have at least 5 drives, and you probably wouldn't notice until you get to 7 or more drives. ... so it might make sense to make mdadm default to converting to the -6 layout... You can request it with "--layout=preserve". > > If so, do you think normalizing would be worth the risk of something > going wrong with that operation? I'm just trying to get a feel for > how much of a difference this makes. Not worth the risk. NeilBrown > > > > mdadm first converts the RAID5 to RAID6 in an instant atomic operation which > > results in the "-6" layout. It then starts a restriping process which > > converts the layout. > > > > If you end up with a -6 layout then something when wrong starting the > > restriping process. > > > > Maybe you used different version of mdadm? There have probably been bugs in > > some versions.. > > > > 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 -- 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
