can a VM's harddisk be faster than the physical disk?

Jan Claeys lists at janc.be
Sat Jan 15 03:34:56 UTC 2011


Stefan Sticht schreef op ma 10-01-2011 om 21:11 [+0100]:
> Dear Ubuntu friends,
> 
> I have a little home-grown box whose VM's harddisk seems to be faster
> than the host's harddisk:
[snip]
> The VM's disk is a qcow2 file on a LVM volume on a RAID-0 over 3 SATA
> disks.  CPU is i7-920. Running Maverick with qemu-kvm 0.13.
> 
> Possible explanations? Is the time in my VM not accurate?

Does your qcow2 file grow as-needed?  If hdparm is reading from unused
diskspace inside the VM, the hard disk emulation in kvm/qemu might be
sending back the same block of zeros all the time without touching any
hardware...


-- 
Jan Claeys





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