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I am setting up a system with two 3TB hard drives as storage backing. As it's a desktop station, I thougth about the following disk setup:

sda
+ /boot with 500MB
+ btrfs for the remaining GBytes
sdb
+ btrfs for all the 3000GB

I then thought about using the single-mode for data on / and create a subvolume for /home (and potentially others) using raid1 as data mode. Is that possible with current (kernel 3.7.X) btrfs? Does anyone have sources for that, I was unable to find anything.

UPDATE: I made a small test setup consisting of two plain files hooked in as loopback devices for playing around. On those files, I created a plain btrfs. Then I did the following:

btrfs subvolume create test
dd if=/dev/urandom of=foo bs=1024 count=1  # use random data to prevent dedup
dd if=/dev/urandom of=test/bar bs=1024 count=1  # use random data to prevent dedup
btrfs balance start -dconvert=raid1 test
btrfs balance start -dconvert=single .
btrfs filesystem df .

That showed the filesystem having all its usage in single mode, instead of partial RAID1 and partial single mode… what did I do wrong?

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up vote 5 down vote accepted

The btrfs balance command applies to filesystems as shown by the help even thought the "filesystem" parameter is optional:

# btrfs balance start --help
usage: btrfs [filesystem] balance start [options] <path>

Until there is a "btrfs subvolume balance" command then I suspect this feature doesn't exist.

(Above based on Btrfs Btrfs v0.19)

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I am just moving to btrfs and I have exactly the same request. The only solution I came up, is the obvious one: just create two separate/independent btrfs filesystemes (i.e. top-level subvolumes), one for each raid-level.

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