Curing Virtualizations’ Disk I/O Bottleneck

Disk fragmentation is bad enough on physical machines, but with virtualization the problem can get much worse:

With physical machines we ran disk defragmentation as part of routine maintenance. But when virtualization arrived, we technologists sometimes overlooked this housekeeping task. Surely, we thought, virtualization somehow gets rid of the channel contention issue, or makes it invisible, or something. It doesn’t help that I/O congestion tends to be highest on very well-utilized host systems, especially virtualization hosts with high resource utilization. Fragmentation is traditionally a physical system problem that creeps up on system administrators over time, causing gradual performance degradation that is difficult to diagnose. That same “slow bleed” effect also occurs on virtual systems, making diagnosis just as difficult as it is with physical servers. The best virtual infrastructure administrators often are the ones most plagued with this problem!

Defragmentation and disk performance optimization are features that you’d naturally expect to be part of the hypervisor, or at least the host operating system, but as of now they’re not. This means you must turn to ingenious third-party developers - for example, Diskeeper - which fortunately can now take on the burden of curing the "slows."