Removing a drive from a Btrfs pool

[GreyGeek]

I have three HD's internally in my laptop. It has two HD ports and I used an HD Caddy to convert the CDROM port to an HD port.

Initially, my first drive was recognized as /dev/sda. The second was recognized sdb. I added additional drives so I could create a RAID1 configuration and have a 3rd drive for archiving Btrfs snapshots.

I created the RAID1 using sda and sdb. When I added the third drive, instead of being designated as sdc, it became sdb and what was sdb became sdc. That's why you want to use UUID's instead of /dev/sdX designations.

Last fall I decided to convert from a two drive RAID1 to a two drive pool in order to increase the storage capacity. Today, I decided to remove sdc from the pool and have everything on my sda drive. Here are the results.

Before removing sdc:

sudo btrfs fi usage /

$
Overall:
    Device size:                   1.36TiB
    Device allocated:            132.03GiB
    Device unallocated:            1.23TiB
    Device missing:                  0.00B
    Used:                        114.99GiB
    Free (estimated):              1.24TiB      (min: 1.24TiB)
    Data ratio:                       1.00
    Metadata ratio:                   1.00
    Global reserve:              512.00MiB      (used: 0.00B)

Data,single: Size:129.00GiB, Used:113.92GiB
   /dev/sda1      64.00GiB
   /dev/sdc       65.00GiB

Metadata,single: Size:3.00GiB, Used:1.07GiB
   /dev/sdc        3.00GiB

System,single: Size:32.00MiB, Used:16.00KiB
   /dev/sdc       32.00MiB

Unallocated:
   /dev/sda1     627.19GiB
   /dev/sdc      630.61GiB

Here I deleted sdc from the pool:

:~$ sudo btrfs device delete /dev/sdc /mnt

and redisplayed the usage:

:~$ sudo btrfs fi usage /

Overall:
    Device size:                 691.19GiB
    Device allocated:            116.03GiB
    Device unallocated:          575.15GiB
    Device missing:                  0.00B
    Used:                        114.97GiB
    Free (estimated):            575.24GiB      (min: 575.24GiB)
    Data ratio:                       1.00
    Metadata ratio:                   1.00
    Global reserve:              512.00MiB      (used: 0.00B)

Data,single: Size:114.00GiB, Used:113.91GiB
   /dev/sda1     114.00GiB

Metadata,single: Size:2.00GiB, Used:1.05GiB
   /dev/sda1       2.00GiB

System,single: Size:32.00MiB, Used:16.00KiB
   /dev/sda1      32.00MiB

Unallocated:
   /dev/sda1     575.15GiB

Now I can reformat what is sdc. and install Bionic on sda, using Btrfs, or course!