As the server virtualization market has matured, hypervisor vendors have added data storage management features to their products, sometimes in conflict with storage vendors. VMware Inc. was first to address storage and continues to lead competitors Citrix Systems Inc. and Microsoft Corp. in data storage management features and functionality.
VMware's virtual storage manager resides within the vCenter management console. The vStorage Virtual Machine File System (VMFS) is a cluster file system that provides optimized virtual machine (VM) storage virtualization. vStorage stores the VM state in a central location, and storage administrators can run multiple, concurrent instances of VMware ESX Server and access the same VM storage. VMware data storage management also includes advanced features such as thin provisioning and hot extension for virtual LUNs, which allows storage managers to expand LUNs at the VMFS level without taking down the LUN. VMware Data Recovery takes VM snapshots and does file-level recovery from virtual machine disk (VMDK) backups.
While VMware used to require its VMFS to support capabilities such as its VMotion live migration feature, its customers can now run VMware with NFS or Raw Device Mapping, which maps virtual servers to storage at the block level.
Citrix XenServer 5.5
Citrix's XenServer 5.5 has limited data storage management capabilities unless you purchase the Citrix Essentials add-on package, which includes the company's StorageLink technology. StorageLink lets storage arrays behave as native XenServer storage, so administrators can provision VM storage directly from the XenServer management console by making features such as thin provisioning, data deduplication and performance optimization that are included with the arrays available.
Microsoft Hyper-V R2
The introduction of Microsoft Hyper-V R2 last October included improvements in the hypervisor's storage capabilities, mostly features that VMware customers were already accustomed to. Data storage managers using Hyper-V can now dynamically add and remove disks from guest operating systems and dynamically expand virtual hard disks (VHDs). Hyper-V R2 also introduced Cluster Shared Volumes, which allow multiple VMs to share LUNs.
Hyper-V R2 with System Center Virtual Machine Manager 2008 R2 also supports Live Storage Migration, which allows LUN-to-LUN migration of storage from one platform to another, although this requires some downtime. VMware Storage VMotion supports similar migration without downtime. Hyper-V also uses the Microsoft System Center Data Protection Manager (DPM) and Microsoft's Volume Shadow Copy Service (VSS) technology for VM snapshots.