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[213.32.242.104]) by smtp.gmail.com with ESMTPSA id n12sm2579793edi.1.2019.09.23.13.24.46 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 23 Sep 2019 13:24:47 -0700 (PDT) From: To: "'Chris Murphy'" Cc: "'Btrfs BTRFS'" References: <000f01d5723b$6e3d0f70$4ab72e50$@gmail.com> In-Reply-To: Subject: RE: BTRFS checksum mismatch - false positives Date: Mon, 23 Sep 2019 22:24:46 +0200 Message-ID: <003f01d5724c$f1adae30$d5090a90$@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Outlook 16.0 Thread-Index: AQDC/7g4S9J6FUg0YRCQl8sHX15RDgIzZwHmqUzwYnA= Content-Language: en-us Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Hi Chris uname: Linux MHPNAS 3.10.105 #24922 SMP Wed Jul 3 16:37:24 CST 2019 x86_64 = GNU/Linux synology_avoton_1815+ btrfs --version = =20 btrfs-progs v4.0 ash-4.3# btrfs device stats . = = = =20 [/dev/mapper/vg1-volume_1].write_io_errs 0 [/dev/mapper/vg1-volume_1].read_io_errs 0 [/dev/mapper/vg1-volume_1].flush_io_errs 0 [/dev/mapper/vg1-volume_1].corruption_errs 1014 [/dev/mapper/vg1-volume_1].generation_errs 0 Concerning self healing? Synology run BTRFS on top of their SHR - which = means, this where there is redundancy (like RAID5 / RAID6). I don't = think they use any BTRFS RAID (likely due to the RAID5/6 issues with = BTRFS). Does that then mean, there is no redundancy / self-healing = available for data?=20 How would you like the log files - in private mail. I assume it is the = kern.log. To make them useful, I suppose I should also pinpoint which = files seem to be intact? I gather it is the "BTRFS: (null) at logical ... " line that indicate = mismatch errors ? Not sure why the state "(null"). Like: 2019-09-22T16:52:09+02:00 MHPNAS kernel: [1208505.999676] BTRFS: (null) = at logical 1123177283584 on dev /dev/vg1/volume_1, sector 2246150816, = root 259, inode 305979, offset 1316306944, length 4096, links 1 (path: = Backup/Virtual Machines/Kan slettes/Smaller Clone of Windows 7 x64 for = win 10 upgrade.vmwarevm/Windows 7 x64-cl1.vmdk) Best Hoegge -----Original Message----- From: Chris Murphy =20 Sent: 2019-09-23 21:12 To: hoegge@gmail.com Cc: Btrfs BTRFS Subject: Re: BTRFS checksum mismatch - false positives On Mon, Sep 23, 2019 at 12:19 PM wrote: > > Dear BTRFS mailing list, > > I'm running BTRFS on my Synology Diskstation and they have referred me = > to the BTRFS developers. If it's a generic question that's fine, but all the development = happening on this list is very recent kernels and btrfs-progs, which is = not typically the case with distribution specific products. > > For a while I have had quite a few (tens - not hundreds) checksum=20 > mismatch errors on my device (around 6 TB data). It runs BTRFS on SHR=20 > (Synology Hybrid Raid). Most of these checksum mismatches, though, do = not seem "real". > Most of the files are identical to the original files (checked by=20 > binary comparison and by recalculated MD5 hashes). > > What can explain that problem? I thought BTRFS only reported checksum=20 > mismatch errors, when it cannot self-heal the files? It'll report them in any case, and also report if they're fixed. There = are different checksum errors depending on whether metadata or data are = affected (both are checksummed). Btrfs can only self-heal with redundant = copies available. By default metadata is duplicated and should be able = to self-heal, but data is not redundant by default. So it'd depend on = how the storage stack layout is created. We need logs though. It's better to have more than less, if you can go = back ~5 minutes from the first report of checksum mismatch error, that's = better than too aggressive log trimming. Also possibly useful: # uname -a # btrfs --version -- Chris Murphy