[PVE-User] BTRFS...

brian mullan bmullan.mail at gmail.com
Tue Feb 2 17:53:51 CET 2016


Gilberto,

I have used btrfs for almost 2 years and like it alot for its features.
I've not used it with proxmox though.

Matter of fact I just changed my machine to use btrfs raid10 (btrfs raid
not mdm raid).   In btrfs this is only 1 command:

reference:  btrfs with multiple devices
<https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices>
example:
# Use raid10 for both data and metadata
mkfs.btrfs -m raid10 -d raid10 /dev/sdb /dev/sdc /dev/sdd /dev/sde


However, I have learned a lot over that time also.

First, I don't think its yet recommended to run KVM on btrfs.  This could
have changed but it would be wise to understand what the concerns were.

I think it had to do with the COW algorithm of btrfs will churn with every
change made to the running kvm 'image" file... causing high cpu etc.

reference:    http://www.linux-kvm.org/page/Tuning_KVM

see the statement at the bottom...
*Don't use the linux filesystem btrfs on the host for the image files. It
will result in low IO performance. The kvm guest may even freeze when high
IO traffic is done on the guest. *

However, LXC containers on the other hand actually work wonderfully with
btrfs as you can specify the LXC container "backingstore" to be btrfs and
cloning, etc becomes almost instantaneous.




*If 'btrfs' is specified, then the target filesystem must be btrfs,
and the  container rootfs will be created as a new subvolume. This
allows snapshotted clones to be created, but also causes rsync
--one-filesystem to treat it as a separate  filesystem.*


So today I have my KVM images run off an ext4 disk but my lxc containers
are on my main btrfs raid10.

Others may have better insight.

Brian
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