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The Five Features that Distinguish Hybrid Storage Arrays from One Another

DCIG has concluded our analysis of 41 hybrid storage arrays for the forthcoming DCIG 2014 Hybrid Storage Array Buyer’s Guide, As we reflected on the data we had collected, there were five features that stood out as distinguishing hybrid storage arrays from one another, and from all-flash arrays or traditional arrays. 
Caching/Tiering Capabilities 
Design and implementation of caching/tiering capabilities is the most significant differentiator between hybrid storage arrays and all-flash or traditional arrays. Providers want to ensure that I/O requests are always satisfied from higher performing cache via tiering, particularly those associated with business critical applications systems. 
Of the 41 arrays we evaluated, 34 can perform dynamic data tiering/caching based on preset system policies or algorithms; while 13 can incorporate user-defined policies and 6 user-defined performance targets. Similarly, management of tiering can be done system-wide on 25 of the 41 arrays, while 33 enable users to manage tiering/caching on a per LUN/volume basis, and 15 on a per VM basis.
Providers employ several strategies to achieve optimum caching/tiering results: 
  • More DRAM cache than in traditional storage arrays 
  • In-line deduplication and/or compression of data in the cache and on disk 
  • Highest performance media for write cache (e.g. NVRAM, SLC, mirrored SSDs) 
  • Metadata stored separately from file data on high performance media 
  • Quality of Service (QoS) policies per VM/LUN/Volume that determine how read and write queues are serviced 
  • Separate and dedicated read & write caches 
  • Multiple physical or logical write caches 
Consistent Application Performance 
Some providers are focused on making their storage smart about application data. In that regard, users can simply rely on the system to do the performance management for them. Conversely, competing providers allow users to specify, measure, and enforce quality of service (QoS) metrics on a per VM/LUN/Volume basis in order to run multiple critical applications with confidence.
Of the 41 arrays we evaluated, 18 indicate that I/O is automatically balanced across all VMs, LUNS, or volumes. Eleven (11) arrays can do QoS based on the user categorizing each VM, LUN or Volume into pre-defined service levels. Eight (8) arrays enable fine-grained QoS management through user-defined targets, guaranteed minimums or maximums on IOPS, bandwidth or response times.
VMware Integration 
Rethinking the storage architecture is driven by virtualization. That rethinking is done based on the largest installed base provider for hypervisors–VMware. In that regard, VMware provides application programming interfaces (API) for provisioning, management, and reporting. It is those APIs that make a difference in how servers and storage work together. Hybrid storage arrays must take advantage of those VMware APIs to deliver maximum performance.
Of the 41 arrays we evaluated, 24 support all VAAI v4 features and 18 supported multiple VAAI v5 API’s. Snapshot integration with vSphere is supported by 27 of the arrays. 
Performance Monitoring 
Visibility into the performance of the storage system is important for troubleshooting application performance problems when they arise and for capacity planning purposes. Integrated performance monitoring capabilities vary widely among providers. Nearly all the vendors indicated that their included tool monitors performance system-wide, while 29 indicated monitoring at the LUN/volume and 12 claim to show performance per virtual machine. 
Included Software 
Some providers sell their arrays with all software features already licensed. This creates one standard hybrid storage array package and reduces the number of decision points in the purchasing process. This simplified approach to licensing also increases the agility of an IT department in responding to changing business requirements compared to the traditional a-la-carte licensing model, and it is yet another aspect of driving administrative overhead out of the storage management process. 
Among the 41 arrays we evaluated, 28 include the snapshot license, 23 the replication license, and 38 the thin provisioning license. Scoring for this Buyer’s Guide acknowledges the business value of included licenses by awarding a more points to products that ship with software features already licensed.
Decisions, Decisions
The five features highlighted in this article come together in a variety of ways to deliver consistent high performance for enterprise applications at a cost that makes sense to a large number of businesses. These five features also give a glimpse into the many decisions that each of the seventeen vendors has made in bringing their hybrid storage arrays to market–and what they understand to be most important to their current and future customers. That these vendors are addressing a real business need is evidenced by the rapid adoption of hybrid storage arrays by normally conservative enterprise IT shops.
DCIG is looking forward to making the DCIG 2014 Hybrid Storage Array Buyer’s Guide available as a tool to aid enterprises in evaluating these storage systems.
Update: The DCIG 2014 Hybrid Storage Array Buyer’s Guide is now available. It may be downloaded for no charge with registration by following this link.

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