The I/O blender effect is a phenomenon in virtualized environments that degrades storage performance.
The I/O blender effect occurs when multiple virtual machines (VMs) all send their input/output (I/O) streams to a hypervisor for processing. Under heavy work loads, I/O processes which might otherwise have been relatively sequential, become random. This increases the read/write activity on disk heads, which in turn, increases latency. This randomization can occur with all virtualization platforms.