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Microsoft isn’t the only hypervisor vendor to use flash-based caching. VMware allows high-speed caching through its vSphere Flash Read Cache feature.
VMware’s approach has a couple of things in common with that of Microsoft’s. VSphere Flash Read Cache is intended to reduce latency by making strategic use of flash storage. The caching process is also completely transparent, and VMs are oblivious to the cache’s existence. Therefore, no cache-related agents are required.
This is where the similarities end. Microsoft’s approach involves building virtual hard disks on storage tiers controlled by the Windows Server OS. In contrast, VMware treats flash storage as a provisionable resource. VSphere allows for the creation of CPU pools and memory pools. Flash-based caching is based on the creation of a logical object called the Virtual Flash Resource.
The Virtual Flash Resource is nothing more than a logical grouping of flash storage capacity (essentially, a pool of SSDs). Even so, there are some important things to know about it:
In case you’re wondering, most Hyper-V deployments are based on the use of shared storage. If all the Hyper-V hosts use the same physical tiered storage, a live migration shouldn’t impact the contents of the cache.
Although the VMware vSphere Flash Read Cache is designed to boost VM performance, the VMs don’t access the cache directly. Instead, a component known as the vSphere Flash Read Cache Infrastructure acts as a broker that controls flash cache usage. The vSphere Flash Read Cache Infrastructure also enforces administrative policies related to the cache.
While the primary job of the vSphere Flash Read Cache Infrastructure is to broker VM cache access, it also allows the hypervisor to utilize the cache through the Virtual Flash Host Swap Cache feature, which replaces vSphere 5.0’s Swap to SSD.
Whether you’re working in a Microsoft or a VMware environment, flash-based caching has the potential to greatly improve VM performance. The key to receiving the greatest benefit from this caching is to understand how your hypervisor uses the cache, then to add flash storage in a way that adheres with the established best practices for your hypervisor.
Source: Associated press