16.07.2015 11:01, Vladimir 'φ-coder/phcoder' Serbinenko пишет: > On 16.07.2015 05:42, Andrei Borzenkov wrote: >> В Wed, 15 Jul 2015 20:05:56 +0200 >> Vladimir 'φ-coder/phcoder' Serbinenko <phco...@gmail.com> пишет: >> >>> On 28.06.2015 20:06, Andrei Borzenkov wrote: >>>> I was looking at implementing detection of outdated RAID members. >>>> Unfortunately it appears to be fundamentally incompatible with lazy >>>> scanning as implemented currently by GRUB. We simply cannot stop >>>> scanning for other copies of metadata once "enough" was seen. Because >>>> any other disk may contain more actual copy which invalidates >>>> everything seen up to this point. >>>> >>>> So basically either we officially admit that GRUB is not able to detect >>>> stale members or we drop lazy scanning. >>>> >>>> Comments, ideas? >>>> >>> We don't need to see all disks to decide that there is no staleness. If >>> you have an array with N devices and you can lose at most K of them, >>> then you can check for staleness after you have seen max(K+1, N-K) >>> drives. Why? >>> >> >> It's not the problem. The problem is what to do if you see disk with >> generation N+1 after you assembled array with generation N. This can >> mean that what we see is old copy and we should through it away and >> start collecting new one. If I read Linux MD code correctly, that is >> what it actually does. And this means we cannot stop scanning even >> after array is complete. >> > While it's true that it's possible that all the members we have seen are > stale, it shouldn't be common and it's not the biggest problem. Biggest > problem is inconsistency. > We can never guarantee of having seen all the disks as they may not be > eeven visible through firmware but it shouldn't stop us from fixing the > inconsistency problem. >> Extreme example is three-pieces mirror where each piece is actually >> perfectly valid and usable by itself so losing two of them still means >> we can continue to work with remaining one. >> > Mirrors get completely assembled in my patch. >
I fixed trivial read error in case of raid1/raid10 (see attached patch). It works in naive testing. We need regression tests for stale data.
From 2611f7a1649e9564cf65b1312bd76e5f3feb3a3e Mon Sep 17 00:00:00 2001 From: Andrei Borzenkov <arvidj...@gmail.com> Date: Mon, 11 Jan 2016 23:41:13 +0300 Subject: [PATCH] Fix reading from RAID1 and RAID10 Need to set error if current disk is stale. --- grub-core/disk/diskfilter.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/grub-core/disk/diskfilter.c b/grub-core/disk/diskfilter.c index 7fea4c0..d779a0a 100644 --- a/grub-core/disk/diskfilter.c +++ b/grub-core/disk/diskfilter.c @@ -782,6 +782,9 @@ read_segment (struct grub_diskfilter_segment *seg, grub_disk_addr_t sector, && err != GRUB_ERR_UNKNOWN_DEVICE) return err; } + else + err = GRUB_ERR_READ_ERROR; + k++; if (k == seg->node_count) k = 0; -- 1.9.1
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