Hi all 

qemu-img create -f qcow2 -o preallocation=metadata  guest 8G
The above command will alllocate all the 8GB to the diskimage. 
means 
[root@t06 p]# ls -lh
total 1.4M
-rw-r--r-- 1 root root 8.1G Mar  7 12:43 guest

is there is any way to allocate metadata to half size or predefined size ?
i.e 4GB will be allocated and rest 4GB can be allocated dynamically 

 
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Pankaj Rawat