Will BTRFS repair or restore data if corrupted?
Hi,
From what I have read BTRFS does replace a bad copy of data with a known good copy (if it has one). Will BTRFS try to repair the corrupt data or will it simply silently restore the data without the user knowing that a file has been "fixed"?
Quoted 3 lines · Waxhead
Hi,
From what I have read BTRFS does replace a bad copy of data with a kn=
own
Quoted 1 line
good copy (if it has one). Will BTRFS try to repair the corrupt data =
or will
Quoted 1 line
it simply silently restore the data without the user knowing that a f=
ile has
Quoted 1 line
been "fixed"?
=46rom what I've seen, it'll quietly restore the data without the user knowing. The only indication would be in dmesg where there should be a message about incorrect checksums and btrfs fixing it automatically.
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Quoted 4 lines · Waxhead
Hi,
From what I have read BTRFS does replace a bad copy of data with a known good copy (if it has one).
Correct.
Quoted 3 lines
Will BTRFS try to repair the corrupt data or will it simply silently restore the data without the user knowing that a file has been "fixed"?
No, it'll just return the good copy and report the failure in the
system logs. If you want to fix the corrupt data, you need to use scrub, which will check everything and fix blocks with failed checksums.
Hugo.
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darkness bind(2) them. Quoted 1 line · Hugo Mills
On Thu, Jan 26, 2012 at 12:27:57AM +0100, Waxhead wrote:
[...]
Quoted 8 lines
Quoted 3 lines
Will BTRFS try to repair the corrupt data or will it simply silently restore the data without the user knowing that a file has been "fixed"?
No, it'll just return the good copy and report the failure in the
system logs. If you want to fix the corrupt data, you need to use scrub, which will check everything and fix blocks with failed checksums.
Since 3.2, btrfs rewrites the corrupt disk block (commit 4a54c8c and f4a8e65 from Jan Schmidt), even without scrub.
Quoted 10 lines · Stefan Behrens
Quoted 1 line · Hugo Mills
On Thu, Jan 26, 2012 at 12:27:57AM +0100, Waxhead wrote:
[...]
Quoted 7 lines
Quoted 3 lines
Will BTRFS try to repair the corrupt data or will it simply silently restore the data without the user knowing that a file has been "fixed"?
No, it'll just return the good copy and report the failure in the
system logs. If you want to fix the corrupt data, you need to use scrub, which will check everything and fix blocks with failed checksums.
Quoted 9 lines
Since 3.2, btrfs rewrites the corrupt disk block (commit 4a54c8c and f4a8e65 from Jan Schmidt), even without scrub.
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So if I for example edit a text file three times and store it I can get the following.
Version1: I currently like cheese
Version2: I currently like onions
Version3: I currently like apples
As far as I understand a disk corruption might result in me suddenly liking onions (or even cheese) instead of apples without any warning except in syslog.?! I really hope I have misunderstood the concept and that there is some error correction codes somewhere.
Quoted 9 lines
So if I for example edit a text file three times and store it I can get the following.
Version1: I currently like cheese
Version2: I currently like onions
Version3: I currently like apples
As far as I understand a disk corruption might result in me suddenly liking onions (or even cheese) instead of apples without any warning except in syslog.?! I really hope I have misunderstood the concept and that there is some error correction codes somewhere.
Yes, you've completely misunderstood the concept :p
There are crc's on each 4k block of data; if one copy fails the checksum, and a second copy is available, and that copy does match, then the good data will be returned and btrfs will overwrite the corrupted copy with the good copy. If there isn't another copy, then an io error will be returned instead.
Quoted 11 lines · cwillu
Quoted 9 lines
So if I for example edit a text file three times and store it I can get the following.
Version1: I currently like cheese
Version2: I currently like onions
Version3: I currently like apples
As far as I understand a disk corruption might result in me suddenly liking onions (or even cheese) instead of apples without any warning except in syslog.?! I really hope I have misunderstood the concept and that there is some error correction codes somewhere.Yes, you've completely misunderstood the concept :p
Quoted 12 lines
There are crc's on each 4k block of data; if one copy fails the checksum, and a second copy is available, and that copy does match, then the good data will be returned and btrfs will overwrite the corrupted copy with the good copy. If there isn't another copy, then an io error will be returned instead.
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Phew... that sounds better :)