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[Qemu-devel] Feature request for qcow v2

From: Anthony Liguori
Subject: [Qemu-devel] Feature request for qcow v2
Date: Sun, 23 Jul 2006 15:51:06 -0500
User-agent: Thunderbird (X11/20060615)


I've been playing with some code to implement an HTTP block device in QEMU. I'll post when I've got something working. As I am building this though, I thought of something that would be nice to have for qcow v2.

What I'd like is essentially a copy-on-read flag. If this flag is set, and there is a base image, then whenever a read occurs to an unallocated sector, the sector is copied from the base (similar to a write) and the sector is allocated.

The idea is that copy-on-read is useful when read is really slow (for instance, with an HTTP block device). This way, you could essentially always use qcow + HTTP so that your block device was locally cached. It seems a bit more elegant than trying to implement a caching mechanism in the HTTP block device.


Anthony Liguori

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