Messages in this thread | | | From | "Otto Meier" <> | Date | Mon, 22 Jan 2001 19:09:37 +0100 | Subject | Re: [PATCH] - filesystem corruption on soft RAID5 in 2.4.0+ |
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With this patch I did rebuilt my raid5 from scratch. So far it still runs in degraded mode to honor the father of invention. System is a SMP Dual Celeron with kernel 2.4.0. I copied 18 Gbyte of data from my backup to it. So far i have not seen any corroption messages. Last time I did that I got a lot of them. Seams that the fix has improved things for me.
Otto
On Mon, 22 Jan 2001 07:47:42 +1100 (EST), 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 >
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