Re: [Qemu-devel] [Qemu-block] [PATCH v1] [RFC] qcow2: add compression type feature

[John Snow <jsnow@redhat.com>]

On 5/16/19 9:48 AM, Denis Plotnikov wrote:
> The patch adds some preparation parts for incompatible compression type
> feature into QCOW2 header that indicates that *all* compressed clusters
> must be (de)compressed using a certain compression type.
> 
> It is implied that the compression type is set on the image creation and
> can be changed only later by image conversion, thus the only compression
> algorithm is used for the image.
> 
> The plan is to add support for ZSTD and then may be something more effective
> in the future.
> 
> ZSTD compression algorithm consumes 3-5 times less CPU power with a
> comparable compression ratio with zlib. It would be wise to use it for
> data compression e.g. for backups.
> 
> The default compression is ZLIB.
> 

(Merely a curiosity:)

Since this is coming from Virtuozzo, I trust that you've had good luck
with ZSTD already in R&D. What do the compression ratios look like in
practice? It's touted as "comparable to zlib" which certainly does sound
quite nice for streaming compression of backups.

I suppose in the worst case it ought to be faster than bandwidth speeds,
so no harm in utilizing it.

> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>