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Date: Tue, 3 Oct 2017 21:11:21 +0000
From: Hugo Mills <hugo@carfax.org.uk>
To: Stephen Nesbitt <snesbitt@aussieswithtails.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: Seeking Help on Corruption Issues
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   Hi, Stephen,

On Tue, Oct 03, 2017 at 08:52:04PM +0000, Stephen Nesbitt wrote:
> Here it i. There are a couple of out-of-order entries beginning at 117. And
> yes I did uncover a bad stick of RAM:
> 
> btrfs-progs v4.9.1
> leaf 2589782867968 items 134 free space 6753 generation 3351574 owner 2
> fs uuid 24b768c3-2141-44bf-ae93-1c3833c8c8e3
> chunk uuid 19ce12f0-d271-46b8-a691-e0d26c1790c6
[snip]
> item 116 key (1623012749312 EXTENT_ITEM 45056) itemoff 10908 itemsize 53
> extent refs 1 gen 3346444 flags DATA
> extent data backref root 271 objectid 24999978 offset 0 count 1
> item 117 key (1621939052544 EXTENT_ITEM 8192) itemoff 10855 itemsize 53
> extent refs 1 gen 3346495 flags DATA
> extent data backref root 271 objectid 21751764 offset 6733824 count 1
> item 118 key (1623012450304 EXTENT_ITEM 8192) itemoff 10802 itemsize 53
> extent refs 1 gen 3351513 flags DATA
> extent data backref root 271 objectid 5724364 offset 680640512 count 1
> item 119 key (1623012802560 EXTENT_ITEM 12288) itemoff 10749 itemsize 53
> extent refs 1 gen 3346376 flags DATA
> extent data backref root 271 objectid 21751764 offset 6701056 count 1

>>> hex(1623012749312)
'0x179e3193000'
>>> hex(1621939052544)
'0x179a319e000'
>>> hex(1623012450304)
'0x179e314a000'
>>> hex(1623012802560)
'0x179e31a0000'

   That's "e" -> "a" in the fourth hex digit, which is a single-bit
flip, and should be fixable by btrfs check (I think). However, even
fixing that, it's not ordered, because 118 is then before 117, which
could be another bitflip ("9" -> "4" in the 7th digit), but two bad
bits that close to each other seems unlikely to me.

   Hugo.

-- 
Hugo Mills             | Great films about cricket: Silly Point Break
hugo@... carfax.org.uk |
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