[Gluster-devel] few queries regarding file snapshot feature in gluster

Vijay Bellur vbellur at redhat.com
Tue Dec 22 23:50:09 UTC 2015

On 12/21/2015 06:47 AM, Prasanna Kumar Kalever wrote:
> Hi Team,
> I have few queries regarding file snapshot feature in gluster
> what are the limitations of Block device translator and qemu-block translator ?
> Are we using them some where ?
> Do we have plans to improve them ?
> Or someone have a design to implement file snapshot feature ?

I have not heard much feedback about these two translators. The 
qemu-block functionality can be handy for exposing virtual block devices 
and due to features like native snapshotting, it could be quite 
interesting in use cases that require virtual block devices.

The qemu-block translator has not been tested of late. A few months back 
I tried mkfs.xfs after attaching the block device and it failed. I did 
not find more time to look into that further.

file snapshotting could be a possibility with dht2 but I don't think 
much work has happened in that direction.

The other possibilities for file snapshotting include reflinks and 
overlay. Given that reflinks support is most probably going to land 
sometime in xfs, we might be able to leverage this feature and explore 
the possibility of providing snapshots with backend filesystems that are 
reflink capable (btrfs, xfs etc.).

> I am really thankful if some one gives more details about qemu-block xlator,
> I don't see enough documentation regarding this :(

qemu-block xlator provides the ability to snapshot files by relying on 
qcow2/qed image formats. what specific details are you looking for?

Avati & Brian probably have the maximum context about this translator.


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