Re: suspected BTRFS errors resulting in file system becoming unrecovable

["Austin S. Hemmelgarn" <ahferroin7@gmail.com>]

On 2016-01-25 09:58, WillIam Thorne wrote:
> Hi
>
> I have a WD 3TB external HD attached over USB to an arm based micro PC (rasp pi). I was experimenting with btrfs for storing email archives but recently encountered some problems which resulted in the filesystem becoming apparently unrecoverable. I’m not an expert and it was quicker to switch back to ext4 and restored from backup so no support needed. Here what appears to be the relevant part of the syslog including the stack trace in case it is useful:
>
> Best
> W
>
> pi@mail /var/log $ btrfs --version
> Btrfs Btrfs v0.19
In general, if you plan to use BTRFS on Debian (or Raspbian), you should 
be building the tools yourself locally, Debian is almost as bad about 
staying up to date as most enterprise distros.
>
> pi@mail /var/log $ uname -a
> Linux mail 4.1.7-v7+ #817 SMP PREEMPT Sat Sep 19 15:32:00 BST 2015 armv7l GNU/Linux
>
> Jan 20 09:42:08 mail kernel: [2762753.507576] usb 1-1.5: reset high-speed USB device number 4 using dwc_otg
> Jan 20 09:43:18 mail kernel: [2762823.972777] sd 0:0:0:0: [sda] UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
> Jan 20 09:43:18 mail kernel: [2762823.972806] sd 0:0:0:0: [sda] Sense Key : 0x2 [current]
> Jan 20 09:43:18 mail kernel: [2762823.972819] sd 0:0:0:0: [sda] ASC=0x3a ASCQ=0x0
> Jan 20 09:43:18 mail kernel: [2762823.972837] sd 0:0:0:0: [sda] CDB: opcode=0x2a 2a 00 00 f7 2c 20 00 00 f0 00
> Jan 20 09:43:18 mail kernel: [2762823.972851] blk_update_request: I/O error, dev sda, sector 16198688
This line right here ^^^ indicates that it was triggered by an issue 
with the USB device.  I don't personally know enough about USB-MSC and 
SCSI to know for certain what is happening, but you should probably scan 
your logs and make sure you're not still getting stuff like this, 
because if you are, you're likely to get data corruption on any 
filesystem on the device.  Based on this, the BTRFS trace you got is 
probably a result of problems with the USB device.
> Jan 20 09:43:18 mail kernel: [2762823.997601] BTRFS: error (device sda1) in btrfs_commit_transaction:2068: errno=-5 IO failure (Error while writing out transaction)
> Jan 20 09:43:18 mail kernel: [2762824.011517] BTRFS info (device sda1): forced readonly
> Jan 20 09:43:18 mail kernel: [2762824.011537] BTRFS warning (device sda1): Skipping commit of aborted transaction.
> Jan 20 09:43:18 mail kernel: [2762824.011576] ------------[ cut here ]------------
> Jan 20 09:43:18 mail kernel: [2762824.011682] WARNING: CPU: 0 PID: 1318 at fs/btrfs/super.c:260 __btrfs_abort_transaction+0xd8/0x128 [btrfs]()
> Jan 20 09:43:18 mail kernel: [2762824.011709] BTRFS: Transaction aborted (error -5)
> Jan 20 09:43:18 mail kernel: [2762824.011717] Modules linked in: cfg80211 rfkill snd_bcm2835 snd_pcm snd_seq snd_seq_device snd_timer snd btrfs xor xor_neon raid6_pq zlib_deflate sg bcm2835_gpiomem uio_pdrv_genirq uio
> Jan 20 09:43:18 mail kernel: [2762824.011790] CPU: 0 PID: 1318 Comm: btrfs-transacti Not tainted 4.1.7-v7+ #817
> Jan 20 09:43:18 mail kernel: [2762824.011797] Hardware name: BCM2709
> Jan 20 09:43:18 mail kernel: [2762824.011832] [<80018440>] (unwind_backtrace) from [<80013e0c>] (show_stack+0x20/0x24)
> Jan 20 09:43:18 mail kernel: [2762824.011852] [<80013e0c>] (show_stack) from [<80558548>] (dump_stack+0x98/0xe0)
> Jan 20 09:43:18 mail kernel: [2762824.011872] [<80558548>] (dump_stack) from [<80026a4c>] (warn_slowpath_common+0x8c/0xc8)
> Jan 20 09:43:18 mail kernel: [2762824.011892] [<80026a4c>] (warn_slowpath_common) from [<80026ac8>] (warn_slowpath_fmt+0x40/0x48)
> Jan 20 09:43:18 mail kernel: [2762824.011971] [<80026ac8>] (warn_slowpath_fmt) from [<7f051790>] (__btrfs_abort_transaction+0xd8/0x128 [btrfs])
> Jan 20 09:43:18 mail kernel: [2762824.012153] [<7f051790>] (__btrfs_abort_transaction [btrfs]) from [<7f082a84>] (btrfs_commit_transaction+0x330/0xd40 [btrfs])
> Jan 20 09:43:18 mail kernel: [2762824.012353] [<7f082a84>] (btrfs_commit_transaction [btrfs]) from [<7f07e95c>] (transaction_kthread+0x174/0x1ec [btrfs])
> Jan 20 09:43:18 mail kernel: [2762824.012463] [<7f07e95c>] (transaction_kthread [btrfs]) from [<80042498>] (kthread+0xe8/0x104)
> Jan 20 09:43:18 mail kernel: [2762824.012481] [<80042498>] (kthread) from [<8000fa58>] (ret_from_fork+0x14/0x3c)
> Jan 20 09:43:18 mail kernel: [2762824.012492] ---[ end trace 1c48a450ca505104 ]---
> Jan 20 09:43:18 mail kernel: [2762824.012505] BTRFS: error (device sda1) in cleanup_transaction:1692: errno=-5 IO failure
> Jan 20 09:43:18 mail kernel: [2762824.022734] BTRFS info (device sda1): delayed_refs has NO entry
The bit about 'transaction aborted' is almost always indicative of an 
error with the storage path (in your case, the USB controller, the USB 
cable, or the USB device), not BTRFS.  That said, something like this 
shouldn't usually cause the FS to be irreparably damaged, although it 
will make the FS unusable until you remount (or possibly until you 
reboot, I'm not certain about the error handling here because I've never 
dealt with it myself).

Now, just a general caution: Avoid using USB storage for persistent 
online storage, there's just to many things that can go wrong, and quite 
a few USB storage controllers are absolute crap.  I understand that this 
can be somewhat tricky with something like a Raspberry Pi, but with 
BTRFS especially, there's not sufficient error recovery in Linux to 
safely use most USB storage devices for anything other than file 
transfers or possibly off-line backups.  That said, there are some 
brands that work well provided they get enough power (I've personally 
had really good results using a SanDisk Cruzer Fit flash drive (the USB 
3.0 version, I've had only intermittent success with the USB 2.0 ones) 
with a Raspberry Pi via a powered hub).