How to move a btrfs volume to a smaller disk

DISCUSSION Hendrik Friedel 3 participants 4 messages Mar 9, 2016 – Mar 11, 2016 Btrfs file system

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Hendrik Friedel

author

2016-03-09 21:46 UTC #0 lore raw

Hello,

I intend to move this subvolume to a new device. btrfs fi show /mnt2/Data_Store/
Label: 'Data_Store' uuid: 0ccc1e24-090d-42e2-9e61-d0a1b3101f93
Total devices 1 FS bytes used 47.93GiB
devid 1 size 102.94GiB used 76.03GiB path /dev/sdb4

(fi usage at the bottom of this message)

The new device (sda4) is 8G smaller unfortunately.
sda 8:0 0 111.8G 0 disk

└─sda4    8:4    0 103.5G  0 part
sdb       8:16   0 119.2G  0 disk
└─sdb4    8:20   0   111G  0 part  /mnt2/Data_Store

Thus, btrfs replace does not work

What would you suggest now to move the FS (it does contain many subvolumes)?

I tried btrfs send /mnt2/Data_Store/read_only_snapshot/ | btrfs receive /mnt/sda4/ but this only created an empty subvolume /mnt/sda4/read_only_snapshot/

So, then
btrfs device add /dev/sda4 /mnt/Data_Store
btrfs balance start /mnt/Data_Store
btrfs device remove /dev/sdb4 /mnt/Data_Store
?

Or is there a better option?

Regards,
Hendrik

btrfs fi usage /mnt2/Data_Store/
Overall:
Device size: 102.94GiB
Device allocated: 74.03GiB
Device unallocated: 28.91GiB
Device missing: 0.00B
Used: 47.96GiB
Free (estimated): 53.24GiB (min: 53.24GiB)
Data ratio: 1.00
Metadata ratio: 1.00
Global reserve: 512.00MiB (used: 0.00B)

Data,single: Size:69.00GiB, Used:44.67GiB
/dev/sdb4 69.00GiB

Metadata,single: Size:5.00GiB, Used:3.29GiB
/dev/sdb4 5.00GiB

System,single: Size:32.00MiB, Used:16.00KiB
/dev/sdb4 32.00MiB

Unallocated:
/dev/sdb4 28.91GiB

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Hugo Mills

2016-03-09 21:50 UTC #1 lore raw

Quoted 12 lines · Hendrik Friedel

Hello,
I intend to move this subvolume to a new device. btrfs fi show /mnt2/Data_Store/
Label: 'Data_Store' uuid: 0ccc1e24-090d-42e2-9e61-d0a1b3101f93
Total devices 1 FS bytes used 47.93GiB
devid 1 size 102.94GiB used 76.03GiB path /dev/sdb4
(fi usage at the bottom of this message)
The new device (sda4) is 8G smaller unfortunately.
sda 8:0 0 111.8G 0 disk

Quoted 7 lines

└─sda4    8:4    0 103.5G  0 part
sdb       8:16   0 119.2G  0 disk
└─sdb4    8:20   0   111G  0 part  /mnt2/Data_Store
Thus, btrfs replace does not work
What would you suggest now to move the FS (it does contain many subvolumes)?

btrfs dev resize to shrink it to (slightly smaller than) the
replacement device, then btrfs replace should work. Then btrfs dev resize max to fill up the replacement device completely.

Hugo.

Quoted 45 lines

I tried btrfs send /mnt2/Data_Store/read_only_snapshot/ | btrfs receive /mnt/sda4/
but this only created an empty subvolume /mnt/sda4/read_only_snapshot/
So, then
btrfs device add /dev/sda4 /mnt/Data_Store
btrfs balance start /mnt/Data_Store
btrfs device remove /dev/sdb4 /mnt/Data_Store
?
Or is there a better option?
Regards,
Hendrik
btrfs fi usage /mnt2/Data_Store/
Overall:
Device size: 102.94GiB
Device allocated: 74.03GiB
Device unallocated: 28.91GiB
Device missing: 0.00B
Used: 47.96GiB
Free (estimated): 53.24GiB (min: 53.24GiB)
Data ratio: 1.00
Metadata ratio: 1.00
Global reserve: 512.00MiB (used: 0.00B)
Data,single: Size:69.00GiB, Used:44.67GiB
/dev/sdb4 69.00GiB
Metadata,single: Size:5.00GiB, Used:3.29GiB
/dev/sdb4 5.00GiB
System,single: Size:32.00MiB, Used:16.00KiB
/dev/sdb4 32.00MiB
Unallocated:
   /dev/sdb4      28.91GiB
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Signature · 4 lines

Hugo Mills             | Well, sir, the floor is yours. But remember, the
hugo@... carfax.org.uk | roof is ours!
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                             The Goons

Hendrik Friedel

author

2016-03-09 22:03 UTC #2 lore raw

Hello Hugo,

thanks for your ultrafast reply.
Unfortunately, it does not work for me:
[root@homeserver mnt2]# btrfs filesystem resize 80G /mnt2/Data_Store/ && btrfs replace start /dev/sdb4 /dev/sda4 /mnt2/Data_Store/ -f && btrfs filesystem resize max /mnt2/Data_Store/ Resize '/mnt2/Data_Store/' of '80G'
ERROR: target device smaller than source device (required 119121379328 bytes)
[root@homeserver mnt2]# btrfs filesystem show /mnt2/Data_Store/
Label: 'Data_Store' uuid: 0ccc1e24-090d-42e2-9e61-d0a1b3101f93
Total devices 1 FS bytes used 47.95GiB
devid 1 size 80.00GiB used 66.03GiB path /dev/sdb4

[root@homeserver mnt2]# lsblk | grep sda4
└─sda4 8:4 0 103.5G 0 part

Greetings,
Hendrik

Quoted 17 lines · Hugo Mills

Quoted 16 lines · Hendrik Friedel
Hello,
I intend to move this subvolume to a new device. btrfs fi show /mnt2/Data_Store/
Label: 'Data_Store' uuid: 0ccc1e24-090d-42e2-9e61-d0a1b3101f93
Total devices 1 FS bytes used 47.93GiB
devid 1 size 102.94GiB used 76.03GiB path /dev/sdb4
(fi usage at the bottom of this message)
The new device (sda4) is 8G smaller unfortunately.
sda 8:0 0 111.8G 0 disk
└─sda4    8:4    0 103.5G  0 part
sdb       8:16   0 119.2G  0 disk
└─sdb4    8:20   0   111G  0 part  /mnt2/Data_Store

Quoted 54 lines

Quoted 3 lines
Thus, btrfs replace does not work
What would you suggest now to move the FS (it does contain many subvolumes)?
btrfs dev resize to shrink it to (slightly smaller than) the
replacement device, then btrfs replace should work. Then btrfs dev resize max to fill up the replacement device completely.
Hugo.
Quoted 45 lines
I tried btrfs send /mnt2/Data_Store/read_only_snapshot/ | btrfs receive /mnt/sda4/
but this only created an empty subvolume /mnt/sda4/read_only_snapshot/
So, then
btrfs device add /dev/sda4 /mnt/Data_Store
btrfs balance start /mnt/Data_Store
btrfs device remove /dev/sdb4 /mnt/Data_Store
?
Or is there a better option?
Regards,
Hendrik
btrfs fi usage /mnt2/Data_Store/
Overall:
Device size: 102.94GiB
Device allocated: 74.03GiB
Device unallocated: 28.91GiB
Device missing: 0.00B
Used: 47.96GiB
Free (estimated): 53.24GiB (min: 53.24GiB)
Data ratio: 1.00
Metadata ratio: 1.00
Global reserve: 512.00MiB (used: 0.00B)
Data,single: Size:69.00GiB, Used:44.67GiB
    /dev/sdb4      69.00GiB
Metadata,single: Size:5.00GiB, Used:3.29GiB
    /dev/sdb4       5.00GiB
System,single: Size:32.00MiB, Used:16.00KiB
    /dev/sdb4      32.00MiB
Unallocated:
    /dev/sdb4      28.91GiB
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Satoru Takeuchi

2016-03-11 03:29 UTC #3 lore raw

In reply to Hendrik Friedel

Quoted 16 lines · Hendrik Friedel

Hello,
I intend to move this subvolume to a new device. btrfs fi show /mnt2/Data_Store/
Label: 'Data_Store' uuid: 0ccc1e24-090d-42e2-9e61-d0a1b3101f93
Total devices 1 FS bytes used 47.93GiB
devid 1 size 102.94GiB used 76.03GiB path /dev/sdb4
(fi usage at the bottom of this message)
The new device (sda4) is 8G smaller unfortunately.
sda 8:0 0 111.8G 0 disk
└─sda4    8:4    0 103.5G  0 part
sdb       8:16   0 119.2G  0 disk
└─sdb4    8:20   0   111G  0 part  /mnt2/Data_Store

Quoted 6 lines

Thus, btrfs replace does not work
What would you suggest now to move the FS (it does contain many subvolumes)?
I tried btrfs send /mnt2/Data_Store/read_only_snapshot/ | btrfs receive /mnt/sda4/ but this only created an empty subvolume /mnt/sda4/read_only_snapshot/

I suspect that you captured snapshot as

==========================
btrfs sub snap -r /mnt2/Data_Store /mnt2/Data_Store/read_only_snapshot
==========================

and /mnt2/Data_Store only contains subvolumes instead of having files/directries directly. Then send/receive work as you said. Probably if you run "ls -li /mnt2/Data_Store", all files have inode 256 (it means subvolume). In addition, all the directories under /mnt2/Data_Store/read_only_snapshot are empty.

It's because "sub snap" only handles one subvolume and doesn't handle subvolumes inside it. So, if you'd like to copy all the data by send/receive, you should capture and send/receive snapshot for each subvolume.

Quoted 6 lines

So, then
btrfs device add /dev/sda4 /mnt/Data_Store
btrfs balance start /mnt/Data_Store
btrfs device remove /dev/sdb4 /mnt/Data_Store
?

balance is not necessary. When you run
device remove /dev/sdb4, then all the contents of /dev/sdb4 migrate to /dev/sda4 properly.

Thanks,
Satoru

Quoted 40 lines

Or is there a better option?
Regards,
Hendrik
btrfs fi usage /mnt2/Data_Store/
Overall:
Device size: 102.94GiB
Device allocated: 74.03GiB
Device unallocated: 28.91GiB
Device missing: 0.00B
Used: 47.96GiB
Free (estimated): 53.24GiB (min: 53.24GiB)
Data ratio: 1.00
Metadata ratio: 1.00
Global reserve: 512.00MiB (used: 0.00B)
Data,single: Size:69.00GiB, Used:44.67GiB
    /dev/sdb4      69.00GiB
Metadata,single: Size:5.00GiB, Used:3.29GiB
    /dev/sdb4       5.00GiB
System,single: Size:32.00MiB, Used:16.00KiB
    /dev/sdb4      32.00MiB
Unallocated:
    /dev/sdb4      28.91GiB
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