Autoextend doesn't work

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Hello, As I saw in documentation, cloudbase-init should autoextend volumes. I have installed Windows Server 2008 R2, then I installed some drivers and after that I installed cloudbase-init and accepted sysprep with shutdown in the end. After shutdown I've added 30GB using qemu-img resize and started my machine, but it hasn't autoextended space - it has just added 30GB as unallocated space.