On Sun, Jan 2, 2011 at 5:10 PM, Leslie Rhorer <lrhorer@xxxxxxxxxxx> wrote: > > Â Â Â ÂOK, I asked this question here before, and I got no answer > whatsoever. ÂI wasn't too concerned previously, but now that I lost the > entire array the last time I tried to do a growth, I am truly concerned. > Would someone please answer my question this time, and perhaps point me > toward a resolution? ÂThe monthly array check just finished on my main > machine. ÂFor many months, this happened at the first of the month and > completed without issue and with zero mismatches. ÂAs of a couple of months > ago, it started to report large numbers of mismatches. ÂIt just completed > this afternoon with the following: > > RebuildFinished /dev/md0 mismatches found: 96614968 > > Â Â Â ÂNow, 96,000,000 mismatches would seem to be a matter of great > concern, if you ask me. ÂHow can there be any, really, when the entire array > - all 11T - was re-written just a few weeks ago? ÂHow can I find out what > the nature of these mismatches is, and how can I correct them without > destroying the data on the array? ÂHow can I look to prevent them in the > future? ÂI take it the monthly checkarray routine (which basically > implements ` echo check > /sys/block/md0/md/sync_action`) does not attempt > to fix any errors it finds? > > Â Â Â ÂI just recently found out md uses simple parity to try to maintain > the validity of the data. ÂI had always thought it was ECC. ÂWith simple > parity it can be difficult or even impossible to tell which data member is > in error, given two conflicting members. ÂWhere should I go from here? ÂCan > I use `echo repair > /sys/block/md0/md/sync_action` with impunity? ÂWhat, > exactly, will this do when it comes across a mismatch between one or more > members? > > RAID6 array > mdadm - v2.6.7.2 > kernel 2.6.26-2-amd64 What commands are you running? Is it just the sync_action or other things in addition? It was my understanding when researching RAID6 last week that the two parity calculations are actually different. Only one of them is simple parity. The the other is part of an advanced math degree. ;-) (According to Wikipedia, not a definitive source for sure...) - Mark -- 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
