Should "System" chunks be included in a btrfs RAID1 balance?

Question

The btrfs wiki RAID1 conversion example gives the following command:

btrfs balance start -dconvert=raid1 -mconvert=raid1 /mnt

There is also the option -s which `man btrfs-balance page defines as:

act on system chunks (requires -f)

So, why not also do -sconvert=raid1 when converting RAID0 to RAID1?

Tom Hale · Answer 1 · 2017-09-23T02:35:05.090

0

Don't pass -f -s, this btrfs mailing list post says it's dangerous.

It is not necessary to pass -s: System chunks are converted to RAID1 automatically:

Before balance:

[tara /]# btrfs fil df /ark 
Data, single: total=2.16TiB, used=2.16TiB
System, DUP: total=8.00MiB, used=256.00KiB
Metadata, DUP: total=7.50GiB, used=5.41GiB
GlobalReserve, single: total=512.00MiB, used=0.00B

After btrfs bal start -dconvert=raid1 -mconvert=raid1 /ark:

[tara /]# btrfs fil df /ark 
Data, RAID1: total=2.16TiB, used=2.16TiB
System, RAID1: total=32.00MiB, used=336.00KiB
Metadata, RAID1: total=14.00GiB, used=5.62GiB
GlobalReserve, single: total=512.00MiB, used=0.00B

Note:

Sytstem, DUP changed to RAID1 above.
GlobalReserve is always single (and not stored on disk).

edited Sep 23 '17 at 02:35

answered Feb 12 '17 at 06:47

Tom Hale

1,105
1
12
24

Why is `GlobalReserve` still single? That would make me worry, especially if its `used` becomes non-zero eventally... – not-a-user Sep 22 '17 at 11:47
@not-a-user Good question. I've updated my answer, please see above. – Tom Hale Sep 23 '17 at 02:31
1

Can confirm this, on Linux 5.5.11: Converted metadata only (`-mconvert=raid1`), left data as raid0 in my case, and System was converted automatically to raid1. – Pianosaurus Aug 31 '22 at 20:23
Converting system blocks to RAID1 are dangerous but this is done implicitly? Does this make sense? – Torsten Bronger Feb 18 '23 at 08:05

Should "System" chunks be included in a btrfs RAID1 balance?

1 Answers1