qemu-img create with preallocation=full and compression_type=zlib
Hi! When running this command on Fedora 35 I get: [#] qemu-img create -o preallocation=full -f qcow2 /var/vm_mail/mytest.qcow2 10GB => Formatting '/var/vm_mail//mytest.qcow2', fmt=qcow2 . . . preallocation=full compression_type=zlib . . . ." Question: When using 'preallocation=full’ I was surprised that the resulting qcow2 image includes the 'compression_type=zlib’ part. Why/when is this compression used when the qcow2 image is fully preallocated? Thanks for input on this! :-) Best regards Richard Taubo
On Tue, Nov 30, 2021 at 02:51:22PM +0100, Richard Taubo wrote:
Hi!
When running this command on Fedora 35 I get: [#] qemu-img create -o preallocation=full -f qcow2 /var/vm_mail/mytest.qcow2 10GB => Formatting '/var/vm_mail//mytest.qcow2', fmt=qcow2 . . . preallocation=full compression_type=zlib . . . ."
Question: When using 'preallocation=full’ I was surprised that the resulting qcow2 image includes the 'compression_type=zlib’ part. Why/when is this compression used when the qcow2 image is fully preallocated?
It doesn't mean the image is currently compressed. Rather it just records the desired compression algorithm for this image, if any future writes were to be told to use compression. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On 30 Nov 2021, at 15:27, Daniel P. Berrangé <berrange@redhat.com> wrote:
On Tue, Nov 30, 2021 at 02:51:22PM +0100, Richard Taubo wrote:
Hi!
When running this command on Fedora 35 I get: [#] qemu-img create -o preallocation=full -f qcow2 /var/vm_mail/mytest.qcow2 10GB => Formatting '/var/vm_mail//mytest.qcow2', fmt=qcow2 . . . preallocation=full compression_type=zlib . . . ."
Question: When using 'preallocation=full’ I was surprised that the resulting qcow2 image includes the 'compression_type=zlib’ part. Why/when is this compression used when the qcow2 image is fully preallocated?
It doesn't mean the image is currently compressed.
Rather it just records the desired compression algorithm for this image, if any future writes were to be told to use compression.
Okay, good to know. Thanks a lot! :-) Best regards Richard Taubo
participants (2)
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Daniel P. Berrangé -
Richard Taubo