cpio to ext4 seems much slower than to ext2, ext3 or xfs

[Daniel P. Berrange]

On Wed, Nov 11, 2009 at 09:05:20PM +0000, Richard W.M. Jones wrote:
> On Wed, Nov 11, 2009 at 01:24:20PM -0600, Eric Sandeen wrote:
> > Anybody got actual numbers?  I don't disagree that mkfs.ext4 is slow in  
> > the default config, but I don't think it should be slower than mkfs.ext3  
> > for the same sized disks.
> 
> Easy with guestfish:
> 
>   $ guestfish --version
>   guestfish 1.0.78
>   $ for fs in ext2 ext3 ext4 xfs jfs ; do guestfish sparse /tmp/test.img 10G : run : echo $fs : sfdiskM /dev/sda , : time mkfs $fs /dev/sda1 ; done
>   ext2
>   elapsed time: 5.21 seconds
>   ext3
>   elapsed time: 7.87 seconds
>   ext4
>   elapsed time: 6.10 seconds
>   xfs
>   elapsed time: 0.45 seconds
>   jfs
>   elapsed time: 0.78 seconds
> 
> Note that because this is using a sparsely allocated disk each write
> to the virtual disk is very slow.  Change 'sparse' to 'alloc' to test
> this with a non-sparse file-backed disk.

You really want to avoid using sparse files at all when doing any kind of
benchmark / performance tests in VMs. The combo of a sparse file store on
a journalling filesystem in the host, w/ virt can cause very pathelogically
bad I/O performance until the file has all its extents fully allocated on
the host FS. So the use of a sparse file may well be exagarating the real
difference in elapsed time between these different mkfs calls in the 
guest.

Regards,
Daniel
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