On Sun, Aug 17, 2014 at 11:16 PM, NeilBrown <neilb@xxxxxxx> wrote: > > Hi all, > There is a risk of data loss with md/raid6 arrays running on Linux since > 2.6.32. > If: > - the array is doubly degraded > - one or both failed devices are being recovered, and > - the array is written to > > then it is possible for data on the array to be lost. The patch below fixes > the problem. If you apply the patch to an older kernel which has separate > handle_stripe5() and handle_stripe6() functions, be sure that patch changes > handle_stripe6(). > > There is no risk to an optimal array or a singly-degraded array. There is > also no risk on a doubly-degraded array which is not recovering a device or > is not receiving write requests. > > If you have data on a RAID6 array, please consider how to avoid corruption, > possibly by applying the patch, possibly by removing any hot spares so > recovery does not automatically start. > > This patch will be sent upstream shortly and will subsequently appear in > future "-stable" kernels. > > NeilBrown > > From f94e37dce722ec7b6666fd04be357f422daa02b5 Mon Sep 17 00:00:00 2001 > From: NeilBrown <neilb@xxxxxxx> > Date: Wed, 13 Aug 2014 09:57:07 +1000 > Subject: [PATCH] md/raid6: avoid data corruption during recovery of > double-degraded RAID6 > > During recovery of a double-degraded RAID6 it is possible for > some blocks not to be recovered properly, leading to corruption. > > If a write happens to one block in a stripe that would be written to a > missing device, and at the same time that stripe is recovering data > to the other missing device, then that recovered data may not be written. > > This patch skips, in the double-degraded case, an optimisation that is > only safe for single-degraded arrays. > > Bug was introduced in 2.6.32 and fix is suitable for any kernel since > then. In an older kernel with separate handle_stripe5() and > handle_stripe6() functions that patch must change handle_stripe6(). > > Cc: stable@xxxxxxxxxxxxxxx (2.6.32+) > Fixes: 6c0069c0ae9659e3a91b68eaed06a5c6c37f45c8 > Cc: Yuri Tikhonov <yur@xxxxxxxxxxx> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > Reported-by: "Manibalan P" <pmanibalan@xxxxxxxxxxxxxx> > Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1090423 > Signed-off-by: NeilBrown <neilb@xxxxxxx> > Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx> ...with a capital "ACK"!. -- 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
