Sluggish scheduling during a long disk copy

[Dan]

Kris Kennaway(kris at FreeBSD.org)@2008.11.09 12:57:16 -0800:
>> could be an issue with ntfs-3g driver
>
> Sounds like it to me.  ntfs-3g uses FUSE, which is a userland filesystem  
> framework.  By design it will have poor I/O performance since every I/O  
> transfer will require multiple trips into and out of the kernel.

The FS performance isn't the issue, the poor interactive performance is.