<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On May 10, 2012, at 1:56 AM, Daniel P. Berrange wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>On Thu, May 10, 2012 at 09:06:58AM +0100, Daniel P. Berrange wrote:<br><font class="Apple-style-span" color="#007b1b"><br></font>I had a quick chat with Kevin Wolf who's the upstream QEMU qcow2 maintainer<br>and he said that 64k is the current recommended cluster size for qcow2.<br>Above this size, the cost of COW becomes higher causing an overall<br>drop in performance.<br><br>Looking at GIT history, Nova has used cluster_size=2M since Vish first<br>added qcow2 support, and there's no mention of why in the commit message.<br>So unless further info comes to light, I'd say we ought to just switch<br>to use qemu-img's default setting of 64K for both Xen and KVM.<br><br></div></blockquote></div><br><div>This is good info. Sounds like we should switch to 64K</div><div><br></div><div>Vish</div></body></html>