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Subject: Re: Virtual Device Support
From: Chris Murphy <lists@colorremedies.com>
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Date: Sun, 19 May 2013 12:22:11 -0600
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On May 19, 2013, at 12:18 PM, Chris Murphy <lists@colorremedies.com> wrote:

> 
> It's not possible to mount regular directories with other file systems. In some ways the btrfs subvolume behaves like a folder. In other ways it acts like a device. If you stat the mount point for btrfs subvolumes, you get a unique device ID for each.

Also a possible use case for btrfs subvolumes as virtual devices, if this isn't already possible or reliable, is in place of LV's for virtual machines. It's very convenient to point a VM to local LVM storage, and have it use an LV which can easily be created, located, and destroyed, and presented to the VM as a single block device. A btrfs subvolume isn't a block device of course, but if it can be pointed to in this fashion it would make it as useful in this scenario as LVs.

Otherwise I have to create another btrfs file system on a qcow2 image which then resides on btrfs. So it's double btrfs which performance wise I think is an undesirable hit.

Chris Murphy