[GLLUG] How can a VM be faster than raw hardware?

Nix nix at esperi.org.uk
Mon Dec 10 12:22:14 UTC 2012

On 9 Dec 2012, Paul Hewlett uttered the following:

> Hi John
> Virtualbox lies - see this link
> http://www.phoronix.com/scan.php?page=article&item=ubuntu_1110_xenkvm&num=7

Well, that's about as reliable as I expect from Phoronix, i.e. only a
grain of truth.

> Virtualbox does not honour sync/fsync requests - your data may be at risk...

VirtualBox does not honour sync/fsync requests iff host I/O caching is
in use. VirtualBox 3.2+ can disable this, whereupon barrier requests,
FUA and the like are respected. QEMU does still appear to do better than
this, in that it can respect flushes (but not barriers) even when host
caching is in use (but not when snapshots are in use) -- but Phoronix is
still over-egging the pudding here.

NULL && (void)

More information about the GLLUG mailing list