Messages in this thread | | | Date | Mon, 22 Jan 2001 12:23:08 +0300 | From | Hans Reiser <> | Subject | Re: [PATCH] - filesystem corruption on soft RAID5 in 2.4.0+ |
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We'll test and get back to you.
Hans
Neil Brown wrote: > > There have been assorted reports of filesystem corruption on raid5 in > 2.4.0, and I have finally got a patch - see below. > I don't know if it addresses everybody's problems, but it fixed a very > really problem that is very reproducable. > > The problem is that parity can be calculated wrongly when doing a > read-modify-write update cycle. If you have a fully functional, you > wont notice this problem as the parity block is never used to return > data. But if you have a degraded array, you will get corruption very > quickly. > So I think this will solve the reported corruption with ext2fs, as I > think they were mostly on degradred arrays. I have no idea whether it > will address the reiserfs problems as I don't think anybody reporting > those problems described their array. > > In any case, please apply, and let me know of any further problems. > > --- ./drivers/md/raid5.c 2001/01/21 04:01:57 1.1 > +++ ./drivers/md/raid5.c 2001/01/21 20:36:05 1.2 > @@ -714,6 +714,11 @@ > break; > } > spin_unlock_irq(&conf->device_lock); > + if (count>1) { > + xor_block(count, bh_ptr); > + count = 1; > + } > + > for (i = disks; i--;) > if (chosen[i]) { > struct buffer_head *bh = sh->bh_cache[i]; > > From my notes for this patch: > > For the read-modify-write cycle, we need to calculate the xor of a > bunch of old blocks and bunch of new versions of those blocks. The > old and new blocks occupy the same buffer space, and because xoring > is delayed until we have lots of buffers, it could get delayed too > much and parity doesn't get calculated until after data had been > over-written. > > This patch flushes any pending xor's before copying over old buffers. > > Everybody running raid5 on 2.4.0 or 2.4.1-pre really should apply this > patch, and then arrange the get parity checked and corrected on their > array. > There currently isn't a clean way to correct parity. > One way would be to shut down to single user, remount all filesystems > readonly, or un mount them, and the pull the plug. > On reboot, raid will rebuild parity, but the filesystems should be > clean. > An alternate it so rerun mkraid giving exactly the write configuration. > This doesn't require pulling the plug, but if you get the config file > wrong, you could loose your data. > > NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
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