Re: Fixing Btrfs Filesystem Full Problems typo?

[Robert White <rwhite@pobox.com>]

On 12/09/2014 02:29 PM, Patrik Lundquist wrote:
 > (stuff depicting a nearly full file system).

Having taken another look at it all, I'd bet (there is not sufficient 
information to be _sure_ from the output you've provided) that you don't 
have the necessary 1Gb free on your disk slice to allocate another data 
extent. The COW portion of some consolidation event is being blocked for 
lack of any place to put the condensed/congealed result of balancing one 
or more of your blocks. You are gong to have to grow your filesystem by 
at least 1 gig to get the balance to complete as-is; or alternately 
remove at least a gig worth of "large files" (e.g. files that are stored 
in a DATA extent as opposed to small ones stored in the metadata).

In the alternate, if you have a "bigger drive" to use, then add that 
device to the file system (q.v. "btrfs device add /dev/sdd1 /muntpoint") 
and then remove the current device (q.v. "btrfs device delete /dev/sdc1 
/mountpoint"). You now have the filesystem on a bigger media where stuff 
can happen correctly.

At _that_ point you can RAID the larger device to equally sized peers 
etc. if your actual goal is to establish full redundancy.

===

If the whole raiding thing was about running out of space, then you are 
actually "done" as soon as you add the second device. It will be used 
automatically, and you can balance over to it directly or not as you see 
fit.

In particular if you have another drive/slice of equal size and you 
intend to spread out onto it, your best choices are ::

btrfs device add /dev/sdd1 /mp

btrfs balance start -dconvert=raid0 -mconvert=dup -sconvert=dup /mp
--or--
btrfs balance start -dconvert=raid0 -mconvert=raid1 -sconvert=raid1 /mp

(the latter is more preservative of information a failed media, but 
since your bulk data isn't being stored redundantly it probably doesn't 
matter which you use.)

Once the second drive is in place you'll have the room you need for the 
balances to finish.

In the second model you'll be spreading your bulk data out onto the two 
drives "evenly" via striping (raid0) and your metadata will be 
duplicated between the two slices.

If you are adding storage and you are _not_ going to be adding it all 
with -dconvert=raid1, it doesn't matter that you don't currently have 
the needed space for a balance to complete on the currently full media. 
If you are trying to raid1 your entire filesystem when you are already 
effectively out of space, you will find no joy. Adding a full media 
raid1 is a no-op for available space.