Btrfs partition made of 3 drives, only one mounted

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1

Hi, Fedora 44 gnome workstation upgraded from a previous release fresh install from Anaconda; selected 3 physical drives as target installation encrypted btrfs mounted / and /home

System has 2 SDD (one for boot) 1 nvme, dedicated to the system (no boot from nvme from bios), 1 hdd for data storage. The 2SSD and 1 nvme are intended as merged system disk for / and /home

Seems the UUID is created ok, but not all the partitions have been mounted with the result of making less drive space available for the system:

luca@joepass:/$ lsblk
NAME                                          MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
sda                                             8:0    0 111.8G  0 disk  
├─sda1                                          8:1    0   600M  0 part  /boot/efi
├─sda2                                          8:2    0     1G  0 part  /boot
└─sda3                                          8:3    0 110.2G  0 part  
  └─luks-bd299009-0c02-45e3-a6b8-f03c443bf88a 252:0    0 110.2G  0 crypt 
sdb                                             8:16   0 111.8G  0 disk  
└─sdb1                                          8:17   0 111.8G  0 part  
  └─luks-8d14ddc8-41d1-4195-bcbc-5369c5ff712c 252:1    0 111.8G  0 crypt 
sdc                                             8:32   0   3.6T  0 disk  
└─sdc1                                          8:33   0   3.6T  0 part  
  └─luks-814c0a2e-503a-462e-be17-fe0dfbb418af 252:3    0   3.6T  0 crypt /mnt/b167553c-b9f9-42f4-a199-664c935fa5ed
zram0                                         251:0    0     8G  0 disk  [SWAP]
nvme0n1                                       259:0    0 465.8G  0 disk  
└─nvme0n1p1                                   259:1    0 465.8G  0 part  
  └─luks-bd2604c4-d369-48e3-8b5a-77480239fbd6 252:2    0 465.7G  0 crypt /home
luca@joepass:/$ 


luca@joepass:/$ sudo btrfs filesystem show
Label: 'fedora'  uuid: d26b6685-ec2e-41d6-b849-9d4ce8c1000d
	Total devices 3 FS bytes used 591.79GiB
	devid    1 size 465.75GiB used 465.74GiB path /dev/mapper/luks-bd2604c4-d369-48e3-8b5a-77480239fbd6
	devid    2 size 110.19GiB used 110.19GiB path /dev/mapper/luks-bd299009-0c02-45e3-a6b8-f03c443bf88a
	devid    3 size 111.77GiB used 111.77GiB path /dev/mapper/luks-8d14ddc8-41d1-4195-bcbc-5369c5ff712c


luca@joepass:/$ mount | grep btrfs
/dev/mapper/luks-bd2604c4-d369-48e3-8b5a-77480239fbd6 on / type btrfs (rw,relatime,seclabel,compress=zstd:1,ssd,discard=async,space_cache=v2,subvolid=257,subvol=/root)
/dev/mapper/luks-bd2604c4-d369-48e3-8b5a-77480239fbd6 on /home type btrfs (rw,relatime,seclabel,compress=zstd:1,ssd,discard=async,space_cache=v2,subvolid=256,subvol=/home)

If I read correctly, / and /home have been created only on nvme disk, other SDD partitions not used/mounted. How can I mount the other 2 SDD physical partition into the main system partition to extend my system storage capacity to the sum of 3 volumes capacity? Many thanks

2

Please use pre-formatted text option </> and not quoting for cli output. It’s difficult to read.

what is the ouput of sudo btrfs filesystem usage / ?
Usually you can add additional devices anytime to a btrfs filesystem
see man btrfs-device.

4

Thank you, and sorry for using the incorrect quoting format:

luca@joepass:/$ sudo btrfs filesystem usage /
[sudo] password for luca: 
Overall:
    Device size:		 687.71GiB
    Device allocated:		 687.71GiB
    Device unallocated:		   3.00MiB
    Device missing:		     0.00B
    Device slack:		     0.00B
    Used:			 594.28GiB
    Free (estimated):		  90.38GiB	(min: 90.38GiB)
    Free (statfs, df):		  90.38GiB
    Data ratio:			      1.00
    Metadata ratio:		      2.00
    Global reserve:		 512.00MiB	(used: 0.00B)
    Multiple profiles:		        no

Data,single: Size:679.69GiB, Used:589.31GiB (86.70%)
   /dev/dm-2	 462.74GiB
   /dev/dm-0	 108.18GiB
   /dev/dm-1	 108.76GiB

Metadata,RAID1: Size:4.00GiB, Used:2.48GiB (62.09%)
   /dev/dm-2	   3.00GiB
   /dev/dm-0	   2.00GiB
   /dev/dm-1	   3.00GiB

System,RAID1: Size:8.00MiB, Used:96.00KiB (1.17%)
   /dev/dm-0	   8.00MiB
   /dev/dm-1	   8.00MiB

Unallocated:
   /dev/dm-2	   1.00MiB
   /dev/dm-0	   1.00MiB
   /dev/dm-1	   1.00MiB
luca@joepass:/$

tried following command:

luca@joepass:/$ sudo btrfs device add /dev/mapper/luks-bd299009-0c02-45e3-a6b8-f03c443bf88a /home
ERROR: /dev/mapper/luks-bd299009-0c02-45e3-a6b8-f03c443bf88a appears to contain an existing filesystem (type=btrfs, label=fedora)
ERROR: use the -f option to force overwrite of /dev/mapper/luks-bd299009-0c02-45e3-a6b8-f03c443bf88a

thanks again.

5

I am not exactly sure what you mean with “only one mounted” as written in the title?

Btrfs is using subvolumes. That means that can share the volume space with other subvolumes. An example is / & /home.

They show the same size while they also share the same space and share the space dynamically.

Is it that what confuses you?

6

That’s normal I think. When the filesystem spans multiple devices, you “mount the multi-device file system by specifying only one member [device]”.

The filesystem itself indeed uses all 3 devices as per sudo btrfs filesystem show.

7

the filessytem is using 3 devices or partitions…

8

It’s part of the device mapper in the kernel, used by LVM. Use dmsetup ls to see what is behind it. source=https://superuser.com/questions/131519/what-is-this-dm-0-device

This might help to better understant:

In the end this is LVM which made this devices and not really BTRFS.

10

LVM? here is no LVM in use. devices are LUKS encrypted…

12

Thank you, I think this explain exactly my concern. Everything started from gnome-disks saying nvme only mounted and used 80% and the 2 ssd not mounted so I thought there was non mounted capacity.

True, that was more accurate than gnome-disk and reassure me the system is making use of the intended resources.

Thank you all for your kind support.