Here are my tests, using stock centos 6.5 qemu-img: [root@server ~]# qemu-img create -f qcow2 image.qcow2 10G Formatting 'image.qcow2', fmt=qcow2 size=10737418240 encryption=off cluster_size=65536 [root@server ~]# qemu-img info image.qcow2 image: image.qcow2 file format: qcow2 virtual size: 10G (10737418240 bytes) disk size: 136K cluster_size: 65536
No options leaves the disk as 136K, it's sparse. [root@server ~]# qemu-img create -f qcow2 -o preallocation=metadata imagepre.qcow2 10G Formatting 'imagepre.qcow2', fmt=qcow2 size=10737418240 encryption=off cluster_size=65536 preallocation='metadata' [root@server ~]# qemu info imagepre.qcow2 -bash: qemu: command not found [root@server ~]# qemu-img info imagepre.qcow2 image: imagepre.qcow2 file format: qcow2 virtual size: 10G (10737418240 bytes) disk size: 1.7M cluster_size: 65536 preallocation=metadata leaves disk as 1.7M, it's also sparse, but a bit bigger. On Fri, Jan 31, 2014 at 11:41 PM, Marcus <shadow...@gmail.com> wrote: > Yes, no_option.img is only 256k in size. it's sparse. > > On Fri, Jan 31, 2014 at 11:38 PM, Yoshikazu Nojima <m...@ynojima.net> wrote: >>>I don't think preallocation=metadata is required for sparse qcow2. >>>Just if you want it to NOT be sparse for metadata. >> >> I think it is required. Please see the output below. Only >> "metadata.img" is a sparse file. >> >> ============== >> [root@ut1-qmb-rd5c test]# qemu-img create -f qcow2 -o >> preallocation=off off.img 3G >> Formatting 'off.img', fmt=qcow2 size=3221225472 encryption=off >> cluster_size=65536 preallocation='off' >> [root@ut1-qmb-rd5c test]# qemu-img create -f qcow2 -o >> preallocation=metadata metadata.img 3G >> Formatting 'metadata.img', fmt=qcow2 size=3221225472 encryption=off >> cluster_size=65536 preallocation='metadata' >> [root@ut1-qmb-rd5c test]# qemu-img create -f qcow2 -o >> preallocation=full full.img 3G >> Formatting 'full.img', fmt=qcow2 size=3221225472 encryption=off >> cluster_size=65536 preallocation='full' >> [root@ut1-qmb-rd5c test]# qemu-img create -f qcow2 no_option.img 3G >> Formatting 'no_option.img', fmt=qcow2 size=3221225472 encryption=off >> cluster_size=65536 >> [root@ut1-qmb-rd5c test]# ls -alhs >> total 3.1G >> 4.0K drwxr-xr-x 2 root root 4.0K Feb 1 06:29 . >> 4.0K dr-xr-x---. 5 root root 4.0K Feb 1 06:19 .. >> 3.1G -rw-r--r-- 1 root root 3.1G Feb 1 06:23 full.img >> 592K -rw-r--r-- 1 root root 3.1G Feb 1 06:21 metadata.img >> 136K -rw-r--r-- 1 root root 256K Feb 1 06:29 no_option.img >> 136K -rw-r--r-- 1 root root 256K Feb 1 06:21 off.img >> ============== >> >> >>>I also remember hearing that either recent qemu-img has a decent >>>preallocation by default now, or that performance has improved such >>>that it doesn't matter. Will need to do some reading to remember, but >>>I think I remember hearing it's not a big deal nowadays. >> >> Ummm. I tested with "qemu-img version 0.12.1," and I confirmed the >> performance of "preallocation=off" is worse than >> "preallocation=metadata", >> but it may be not true with latest qemu. I will test it. >> >> Thank you for your comment! >> >> Regards, >> >> >> 2014-01-31 Marcus <shadow...@gmail.com>: >>> I don't think preallocation=metadata is required for sparse qcow2. >>> Just if you want it to NOT be sparse for metadata. >>> >>> I also remember hearing that either recent qemu-img has a decent >>> preallocation by default now, or that performance has improved such >>> that it doesn't matter. Will need to do some reading to remember, but >>> I think I remember hearing it's not a big deal nowadays. >>> >>> On Fri, Jan 31, 2014 at 10:04 PM, Yoshikazu Nojima <m...@ynojima.net> wrote: >>>> Hello Nux, >>>> >>>> Thank you for your comment. I will prepare feature specification. >>>> >>>> Regards, >>>> >>>> 2014-01-31 Nux! <n...@li.nux.ro>: >>>>> On 31.01.2014 20:24, Yoshikazu Nojima wrote: >>>>>> >>>>>> Afternoon All, >>>>>> >>>>>> Is there anyone working on adding volume provisioning method option? >>>>>> As you know, thin provisioning of a volume save consumption of a >>>>>> storage, and fat provisioning improves IOPS performance. >>>>>> Especially, Qcow2 can save storage consumption and achive relatively >>>>>> better performance than default by provisioning a volume with an >>>>>> option "preallocation=metadata", which makes an image file a sparse >>>>>> file. >>>>>> >>>>>> http://itscblog.tamu.edu/improve-disk-io-performance-in-kvm/#.232---preallocation >>>>>> >>>>>> Any thoughts about this? >>>>>> If it is ok, I will write a feature specification on confluence and >>>>>> start implementation. >>>>>> >>>>>> Regards, >>>>>> Noji >>>>>> >>>>>> >>>>>> Yoshikazu Nojima <m...@ynojima.net> >>>>> >>>>> >>>>> Hello, >>>>> >>>>> I thought preallocation=metadata is common practice since years. Now I >>>>> find >>>>> out ACS doesn't actually use it? >>>>> If so, this is really _bad_ and needs to be fixed ASAP... >>>>> >>>>> Thanks Noji >>>>> >>>>> -- >>>>> Sent from the Delta quadrant using Borg technology! >>>>> >>>>> Nux! >>>>> www.nux.ro
