Re: How to remove missing device on RAID1?

[Kyle Manna <2bluesc@gmail.com>]

Thanks for the follow-up Duncan, that makes sense.  I assumed I was
doing something wrong.

I downloaded the devel branch of of btrfs-progs and got it running
before I saw the need for a kernel patch and decided to wait.

For anyone following this later, I needed to use the following to get
the missing device ID:

btrfs device usage <path>
ᐧ

On Tue, Oct 20, 2015 at 1:58 PM, Duncan <1i5t5.duncan@cox.net> wrote:
> Kyle Manna posted on Tue, 20 Oct 2015 10:24:48 -0700 as excerpted:
>
>> Hi all,
>>
>> I have a collection of three (was 4) 1-2TB devices with data and
>> metadata in a RAID1 mirror.  Last night I was struck by the Click of
>> Death on an old Samsung drive.
>>
>> I removed the device from the system, rebooted and mounted the volume
>> with `-o degraded` and the file system seems fine and usable.  I'm
>> waiting on a replacement, drive but want to remove the old drive and
>> re-balance in the meantime.
>>
>> How do I remove the missing device?  I tried the `btrfs device delete
>> missing /mnt` but was greeted with "ERROR: missing is not a block
>> device".  A quick look at that btrfs-progs git repo shows that
>> `stat("missing")` is called, which of course fails since missing isn't a
>> block device.  Nothing other then `btrfs replace` seemed intuitive and
>> all the docs mention the older command.  What's the move?
>>
>> Thanks!
>> - Kyle
>>
>> Versions:
>> Kernel: 4.2.3-1-ARCH
>> btrfs-progs: 4.2.2-1 ᐧ
>
> I believe the current advice given here (that you were likely trying to
> follow, wrapped link)...
>
> https://btrfs.wiki.kernel.org/index.php/
> Using_Btrfs_with_Multiple_Devices#Replacing_failed_devices
>
> ... is dated and no longer works due to code change some time in the past.
>
> There's a set of (very) recent patches, to the kernel and userspace both
> (I just updated userspace and it's in the git devel-branch v4.2.3-49-
> g4db87a1 I just built, kernelspace, I don't see it in linus-mainline yet,
> so I'd guess it's in the btrfs-integration patches, to land in the v4.4
> commit window if not in 4.3 as it's getting late in the cycle for that.
>
> btrfs fi show <path>
>
> That will list the btrfs component devices together with their devids.
>
> Then use the appropriate devid like so:
>
> btrfs dev del <devid> <path>
>
> The -progs commit is d462081f, by Anand Jain, titled:
>
> btrfs-progs: Introduce device delete by devid
>
> According to it, the required kernel commit (title only listed) is
> similar:
>
> Btrfs: Introduce device delete by devid
>
> You can probably find them on-list if you wish to cherry-pick them into a
> current version.
>
> --
> Duncan - List replies preferred.   No HTML msgs.
> "Every nonfree program has a lord, a master --
> and if you use the program, he is your master."  Richard Stallman
>
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