trouble replacing second disk from pair

trouble replacing second disk from pair

[Rory Campbell-Lange]

We're trying to upgrade the disks in a btrfs pair, and I have successfully replaced one of them using btrfs replace. I presently have 

Label: 'btrfs-bkp'  uuid: da90602a-b98e-4f0b-959a-ce431ac0cdfa
	Total devices 2 FS bytes used 700.29GiB
	devid    2 size 2.73TiB used 1.73TiB path /dev/mapper/cdisk4
	devid    3 size 2.73TiB used 1.75TiB path /dev/mapper/cdisk2

I'd like to get rid of cdisk2 and replace it with a new disk.

However I'm unable to mount cdisk4 (the new disk) in degraded mode to allow me to similarly replace cdisk2 as I previously did for cdisk3. Is this because some of the data in only on cdisk2? If so I'd be grateful to 
know how to ensure the two disks have the same data and to allow cdisk2 to be replaced.

Regards
Rory

# btrfs filesystem usage /bkp

Overall:
    Device size:		   5.46TiB
    Device allocated:		   3.49TiB
    Device unallocated:		   1.97TiB
    Device missing:		     0.00B
    Used:			   1.37TiB
    Free (estimated):		   2.04TiB	(min: 2.04TiB)
    Data ratio:			      2.00
    Metadata ratio:		      1.91
    Global reserve:		 512.00MiB	(used: 0.00B)

Data,single: Size:1.00GiB, Used:1.00MiB
   /dev/mapper/cdisk2	   1.00GiB

Data,RAID1: Size:1.73TiB, Used:691.24GiB
   /dev/mapper/cdisk2	   1.73TiB
   /dev/mapper/cdisk4	   1.73TiB

Data,DUP: Size:8.00GiB, Used:7.30GiB
   /dev/mapper/cdisk2	  16.00GiB

Metadata,single: Size:1.00GiB, Used:0.00B
   /dev/mapper/cdisk2	   1.00GiB

Metadata,RAID1: Size:9.00GiB, Used:1.75GiB
   /dev/mapper/cdisk2	   9.00GiB
   /dev/mapper/cdisk4	   9.00GiB

Metadata,DUP: Size:1.00GiB, Used:10.03MiB
   /dev/mapper/cdisk2	   2.00GiB

System,single: Size:32.00MiB, Used:224.00KiB
   /dev/mapper/cdisk2	  32.00MiB

System,RAID1: Size:32.00MiB, Used:192.00KiB
   /dev/mapper/cdisk2	  32.00MiB
   /dev/mapper/cdisk4	  32.00MiB

System,DUP: Size:32.00MiB, Used:0.00B
   /dev/mapper/cdisk2	  64.00MiB

Unallocated:
   /dev/mapper/cdisk2	 998.39GiB
   /dev/mapper/cdisk4	1018.49GiB

Re: trouble replacing second disk from pair

[Roman Mamedov]

On Wed, 8 Dec 2021 12:40:14 +0000
Rory Campbell-Lange <rory@campbell-lange.net> wrote:

> We're trying to upgrade the disks in a btrfs pair, and I have successfully replaced one of them using btrfs replace. I presently have 
> 
> Label: 'btrfs-bkp'  uuid: da90602a-b98e-4f0b-959a-ce431ac0cdfa
> 	Total devices 2 FS bytes used 700.29GiB
> 	devid    2 size 2.73TiB used 1.73TiB path /dev/mapper/cdisk4
> 	devid    3 size 2.73TiB used 1.75TiB path /dev/mapper/cdisk2
> 
> I'd like to get rid of cdisk2 and replace it with a new disk.
> 
> However I'm unable to mount cdisk4 (the new disk) in degraded mode to allow me to similarly replace cdisk2 as I previously did for cdisk3. Is this because some of the data in only on cdisk2? If so I'd be grateful to 
> know how to ensure the two disks have the same data and to allow cdisk2 to be replaced.

Looks like you need to ensure everything is RAID1 first:

  btrfs balance start -dconvert=raid1,soft /bkp
  btrfs balance start -mconvert=raid1,soft /bkp
  btrfs balance start -sconvert=raid1,soft /bkp

It might warn you about operating on system chunks, but I believe this still
needs to be done. 

If still unable to mount after that, then post what mount command do you use
and which messages you get in dmesg.

-- 
With respect,
Roman

Re: trouble replacing second disk from pair

[Rory Campbell-Lange]

On 08/12/21, Roman Mamedov (rm@romanrm.net) wrote:
> On Wed, 8 Dec 2021 12:40:14 +0000
> Rory Campbell-Lange <rory@campbell-lange.net> wrote:
> 
> > We're trying to upgrade the disks in a btrfs pair, and I have successfully replaced one of them using btrfs replace. I presently have 
> > 
> > Label: 'btrfs-bkp'  uuid: da90602a-b98e-4f0b-959a-ce431ac0cdfa
> > 	Total devices 2 FS bytes used 700.29GiB
> > 	devid    2 size 2.73TiB used 1.73TiB path /dev/mapper/cdisk4
> > 	devid    3 size 2.73TiB used 1.75TiB path /dev/mapper/cdisk2
> > 
> > I'd like to get rid of cdisk2 and replace it with a new disk.
> > 
> > However I'm unable to mount cdisk4 (the new disk) in degraded mode to allow me to similarly replace cdisk2 as I previously did for cdisk3. Is this because some of the data in only on cdisk2? If so I'd be grateful to 
> > know how to ensure the two disks have the same data and to allow cdisk2 to be replaced.
> 
> Looks like you need to ensure everything is RAID1 first:
> 
>   btrfs balance start -dconvert=raid1,soft /bkp
>   btrfs balance start -mconvert=raid1,soft /bkp
>   btrfs balance start -sconvert=raid1,soft /bkp
> 
> It might warn you about operating on system chunks, but I believe this still
> needs to be done. 

I wasn't able to run system chunks (-s) on btrfs 4.20.1-2 (debian) without
forcing it:

    ERROR: Refusing to explicitly operate on system chunks.
    Pass --force if you really want to do that.

Happily everything worked fine after running the data and metadata balances.

Thanks very much indeed for the advice.

Rory

Re: trouble replacing second disk from pair

[Zygo Blaxell]

On Wed, Dec 08, 2021 at 05:21:51PM +0000, Rory Campbell-Lange wrote:
> On 08/12/21, Roman Mamedov (rm@romanrm.net) wrote:
> > On Wed, 8 Dec 2021 12:40:14 +0000
> > Rory Campbell-Lange <rory@campbell-lange.net> wrote:
> > 
> > > We're trying to upgrade the disks in a btrfs pair, and I have successfully replaced one of them using btrfs replace. I presently have 
> > > 
> > > Label: 'btrfs-bkp'  uuid: da90602a-b98e-4f0b-959a-ce431ac0cdfa
> > > 	Total devices 2 FS bytes used 700.29GiB
> > > 	devid    2 size 2.73TiB used 1.73TiB path /dev/mapper/cdisk4
> > > 	devid    3 size 2.73TiB used 1.75TiB path /dev/mapper/cdisk2
> > > 
> > > I'd like to get rid of cdisk2 and replace it with a new disk.
> > > 
> > > However I'm unable to mount cdisk4 (the new disk) in degraded mode to allow me to similarly replace cdisk2 as I previously did for cdisk3. Is this because some of the data in only on cdisk2? If so I'd be grateful to 
> > > know how to ensure the two disks have the same data and to allow cdisk2 to be replaced.
> > 
> > Looks like you need to ensure everything is RAID1 first:

You definitely need these two:

> >   btrfs balance start -dconvert=raid1,soft /bkp
> >   btrfs balance start -mconvert=raid1,soft /bkp

but not this one:

> >   btrfs balance start -sconvert=raid1,soft /bkp
> > 
> > It might warn you about operating on system chunks, but I believe this still
> > needs to be done. 
> 
> I wasn't able to run system chunks (-s) on btrfs 4.20.1-2 (debian) without
> forcing it:
> 
>     ERROR: Refusing to explicitly operate on system chunks.
>     Pass --force if you really want to do that.

-m implies -s.  In normal use, there is never a reason to have different
profiles for metadata and system, so balance refuses to do it.

-s is useful to set up some scenarios for developer testing (though even
that could be achieved with -mconvert=...,vrange=... without needing a
special option).

The manual could be clearer on this.

> Happily everything worked fine after running the data and metadata balances.
> 
> Thanks very much indeed for the advice.
> 
> Rory

Re: trouble replacing second disk from pair

[Roman Mamedov]

On Wed, 8 Dec 2021 13:01:40 -0500
Zygo Blaxell <ce3g8jdj@umail.furryterror.org> wrote:

> -m implies -s.  In normal use, there is never a reason to have different
> profiles for metadata and system

Then there appears to be no reason to have "system" user-visible as a separate
chunk type.

-- 
With respect,
Roman