VMware vSphere 4 supports storage thin provisioning. Thin provisioning for VMware vSphere is a technology that redefines how storage space is allocated to virtual disks. Previously, administrators needed to estimate ho much storage space their virtual disks would take up to support current usage and future growth, and pre-allocate that entire storage space for each disk. Thin provisioning, in contrast, allows virtual disks to use only the amount of storage space they currently need. It is kind of like memory over commit for disk storage.

Anyway, thin provisioning *could* have a possible negative performance impact due to the overhead of allocating more disk space as the VM needs it. VMware recently released a white paper surrounding the performance of VMs when using thin provisioning in a production environment. The white paper talks about I/O-Intensive workloads, file copy workloads, and performance recommendations.

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Technorati : Performance, SAN, Thin Provisioning, VMware
Del.icio.us : Performance, SAN, Thin Provisioning, VMware