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Managing storage for virtual servers

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Use hardware acceleration and APIs

Many vendors (including the top six storage vendors: Dell Inc., EMC Corp., Hewlett-Packard [HP] Co., Hitachi Data Systems, IBM and NetApp Inc.) today support hardware acceleration of virtualization I/O. This is implemented through API interfaces in the hypervisor, such as vStorage APIs for Array Integration (VAAI). VAAI offloads some of the “heavy lifting” from the hypervisor by letting the storage array choose the best way to perform key operations, such as sub-LUN locking, bulk copying and zeroing out ranges of data. Most recently, in vSphere 5, VMware added the thin reclaim feature, which lets the hypervisor release deleted storage from thin provisioned LUNs without directly writing data to deleted blocks.

Offloading storage management tasks to the array provides numerous benefits. First, it reduces the workload on the hypervisor, lessening the CPU load and traffic across the storage network. Second, it lets the storage array optimize and prioritize I/O-intensive operations that may be best achieved internally within the array. As the leading hypervisor vendor, VMware has developed a number of APIs, including vStorage APIs for Data Protection (VADP) and vStorage APIs for Storage Awareness (VASA). VASA is of increasing importance in the delivery of scalable storage environments, providing configuration information to the hypervisor about storage LUNs, including replication and performance metrics.

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Configure for performance

When delivering I/O to virtual environments, performance is everything. Typically, virtual environments create more random workloads, making the work of optimizing I/O workloads much harder for the array. There are techniques that can be employed to ensure performance is delivered optimally, including:

  • Wide striping. This involves spreading I/O across as many physical disk spindles as possible. Wide striping can be achieved by using large RAID groups (being mindful of rebuild times for disk failures) or by concatenating RAID groups into storage pools. This technique is applicable to both file- and block-based storage platforms.
  • Dynamic tiering. Like any storage environment, virtual servers will have I/O “hotspots,” data that generates a large proportion of the I/O workload. Hotspot areas can be difficult to predict, so platforms that offer dynamic tiering provide an automated way to ensure the hottest data stays on the fastest disk. This technique is particularly useful where virtual machines have been cloned from a single master image.

This was first published in April 2012

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