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Buddlespit

Member

From: Chesapeake, Va.

Registered: 2014-02-07

Posts: 501

BTRFS and multiple disks/partitions

I've spent the past week trying to read up on btrfs and multiple disks. I'm now very confused. What I want to do (if possible) is convert two ext4 partitions to btrfs partitions, then join the two btrfs partitions, sharing the disk space between the two partitions.

My current partition scheme on my server:

$ lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0   1.8T  0 disk 
└─sda1   8:1    0   1.8T  0 part /shares
sdb      8:16   0 232.9G  0 disk 
├─sdb1   8:17   0   226G  0 part /
└─sdb2   8:18   0   6.9G  0 part [SWAP]
sdc      8:32   0 931.5G  0 disk 
└─sdc1   8:33   0 931.5G  0 part /home

and the disk space used:

$ discus
Mount           Total         Used         Free       Prcnt      Graph
/sys                0 KB         0 KB         0 KB     0.0%   [----------]
/dev            1.89 gig         0 KB     1.89 gig     0.0%   [----------]
+l/security         0 KB         0 KB         0 KB     0.0%   [----------]
/dev/shm        1.93 gig         0 KB     1.93 gig     0.0%   [----------]
/run            1.93 gig       492 KB     1.93 gig     0.0%   [----------]
+/fs/cgroup     1.93 gig         0 KB     1.93 gig     0.0%   [----------]
+up/systemd         0 KB         0 KB         0 KB     0.0%   [----------]
+/fs/pstore         0 KB         0 KB         0 KB     0.0%   [----------]
+oup/memory         0 KB         0 KB         0 KB     0.0%   [----------]
+up/net_cls         0 KB         0 KB         0 KB     0.0%   [----------]
+roup/bfqio         0 KB         0 KB         0 KB     0.0%   [----------]
+oup/cpuset         0 KB         0 KB         0 KB     0.0%   [----------]
+up/freezer         0 KB         0 KB         0 KB     0.0%   [----------]
+roup/blkio         0 KB         0 KB         0 KB     0.0%   [----------]
+up/devices         0 KB         0 KB         0 KB     0.0%   [----------]
/             222.33 gig     4.79 gig   206.23 gig     2.2%   [----------]
+infmt_misc         0 KB         0 KB         0 KB     0.0%   [----------]
/tmp            1.93 gig         4 KB     1.93 gig     0.0%   [----------]
+/hugepages         0 KB         0 KB         0 KB     0.0%   [----------]
+dev/mqueue         0 KB         0 KB         0 KB     0.0%   [----------]
+rnel/debug         0 KB         0 KB         0 KB     0.0%   [----------]
+nel/config         0 KB         0 KB         0 KB     0.0%   [----------]
/home         916.77 gig   294.63 gig   575.55 gig    32.1%   [***-------]
/shares          1.79 TB      1.17 TB   540.51 gig    65.4%   [*******---]
+/user/1000    395.1 meg         0 KB    395.1 meg     0.0%   [----------]

I want to combine /dev/sda1 and /dev/sdc1 (/home and /shares) because I'm slowly using up the space on /dev/sda1 (/shares) and the space on /dev/sdc1 (/home) has stayed about the same for the past 4 months. I guess I'm looking for a way to combine the two disks into a single BTRFS array with two partitions on it without loosing any data currently stored on both disks. Does this make sense?

Before anyone comments about the space available on my root drive (/dev/sdb1), I'm planning to shrink the partition, then 'dd' it (along with the swap) to a 32GB SSD that I have laying around, waiting for just this purpose.

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Hw-Probe

WorMzy

Administrator

From: Scotland

Registered: 2010-06-16

Posts: 12,513

Website

Re: BTRFS and multiple disks/partitions

Are you trying to convert the filesystems in place? Never done that, (I recommend making clean btrfs partitons rather than converting).

You can add multiple "devices"* to a single btrfs filesystem (I have this set up on a couple of my machines), but I don't know how btrfs handles adding a second filesystem with files on it to another btrfs filesystem. I'd recommend that you test this out on a virtual machine first (or loop devices might work).

*This can be disks, or partitions

Last edited by WorMzy (2015-04-18 21:29:33)

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Buddlespit

Member

From: Chesapeake, Va.

Registered: 2014-02-07

Posts: 501

Re: BTRFS and multiple disks/partitions

Ya, I guess that'll be the way to go

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Hw-Probe

ANOKNUSA

Member

Registered: 2010-10-22

Posts: 2,141

Re: BTRFS and multiple disks/partitions

@Buddlespit, You can certainly get the setup you want pretty easily, but as WorMzy said it would be easier and safer to back up all the data, create the BTRFS filesystem and copy everything back. You can use BTRFS subvolumes instead of partitions, and the space will be shared across both disks. Just don't use RAID since your disks are different sizes.

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