Re: Data recovery from a linear multi-disk btrfs file system

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

On 2016-07-15 05:51, Matt wrote:
> Hello
>
> I glued together 6 disks in linear lvm fashion (no RAID) to obtain one large file system (see below).  One of the 6 disk failed. What is the best way to recover from this?
>
> Thanks to RAID1 of the metadata I can still access the data residing on the remaining 5 disks after mounting ro,force.  What I would like to do now is to
>
> 1) Find out the names of all the files with missing data
> 2) Make the file system fully functional (rw) again.
>
> To achieve 2 I wanted to move the data of the disk. This, however, turns out to be rather difficult.
>  - rsync does not provide a immediate time-out option in case of an IO error
>  - Even when I set the time-out for dd_rescue to a minimum, the transfer speed is still way too low to move the data
>  (> 15TB) off the file system.
> Both methods are too slow to move off the data within a reasonable time frame.
>
> Does anybody have a suggestion how to best recover from this? (Our backup is incomplete).
> I am looking for either a tool to move off the  data — something which gives up immediately in case of IO error and log the affected files.
> Alternatively I am looking for a btrfs command like  “ btrfs device delete missing “ for a non-RAID multi-disk btrfs filesystem.
> Would some variant of  "btrfs balance" do something helpful?
>
> Any help is appreciated!
>
> Regards,
> Matt
>
> # btrfs fi show
> Label: none  uuid: d82fff2c-0232-47dd-a257-04c67141fc83
> 	Total devices 6 FS bytes used 16.83TiB
> 	devid    1 size 3.64TiB used 3.47TiB path /dev/sdc
> 	devid    2 size 3.64TiB used 3.47TiB path /dev/sdd
> 	devid    3 size 3.64TiB used 3.47TiB path /dev/sde
> 	devid    4 size 3.64TiB used 3.47TiB path /dev/sdf
> 	devid    5 size 1.82TiB used 1.82TiB path /dev/sdb
> 	*** Some devices missing
>
>
> \x16# btrfs fi df /work
> Data, RAID0: total=18.31TiB, used=16.80TiB
> Data, single: total=8.00MiB, used=8.00MiB
> System, RAID1: total=8.00MiB, used=896.00KiB
> System, single: total=4.00MiB, used=0.00B
> Metadata, RAID1: total=34.00GiB, used=30.18GiB
> Metadata, single: total=8.00MiB, used=0.00B
> GlobalReserve, single: total=512.00MiB, used=0.00B
The tool you want is `btrfs restore`.  You'll need somewhere to put the 
files from this too of course.  That said, given that you had data in 
raid0 mode, you're not likely to get much other than very small files 
back out of this, and given other factors, you're not likely to get what 
you would consider reasonable performance out of this either.

Your best bet to get a working filesystem again would be to just 
recreate it from scratch, there's not much else that can be done when 
you've got a raid0 profile and have lost a disk.