Small to medium sized businesses aren’t in the enterprise category but their users certainly have enterprise expectations. Storage Switzerland Founder George Crump calls it the “Facebook-ing of IT”, in reference to the always-on, always-available services that big cloud and social media companies have created thanks to their advanced infrastructures and enormous IT investments. These services are as reliable as a public utility, a fact that has ‘trained’ the data consuming public to expect this from all their on-line and internal IT experiences.
Instant response and snappy performance is also becoming expected. As users get accustomed to the latency of the flash drives in their own computers (or the lack of latency) they start to expect that kind of performance with company infrastructure as well, which for IT means the integration flash technology into their storage infrastructure. Hybrid flash systems can bring this performance to the SMB in a shared storage format that’s easier to implement and easier to cost justify than putting flash into each server.
But combining disk drives and flash means the system needs a mechanism to make sure the right data is on flash at the right time, typically a caching process. When this doesn’t happen performance can become unpredictable, something that’s especially challenging in virtual server environments. While it’s not often talked about by vendors, the reality of hybrid systems is that at some point the requested data won’t be in flash which leads to that unpredictability.
To address this Fusion-io just released version 3.0 of their ioControl hybrid storage system, which integrates some interesting QoS-driven features that may help address the issues of accurate data placement and predictable performance in hybrid arrays.
QoS-driven Data Placement
ioControl 3.0 uses QoS and a technology they call Dynamic Data Placement (DDP) to minimize the impact of not having the requested data in flash. Users start by setting the QoS desired for each data volume – either “mission critical”, “business critical” or “non-critical” – along with a minimum performance level. When an application is requesting data that’s not in the cache, the system responds in accordance with its QoS designation.
Mission critical data is immediately moved into flash and the read cache is aggressively pre-populated with that data. Business critical data is also moved back into flash but less aggressively, assuming the performance levels set for those volumes aren’t met by disk storage. Finally, if a cache miss occurs to a non-critical volume nothing is moved. By making sure that non-critical data, like home directories stays out of the caching area, it leaves more premium flash real estate for those applications that do.
Not all data is created equally and by using some intelligence to prioritize the service each volume gets, users can keep the most important data in flash. But just as importantly, the system can also respond appropriately to the enviable cache misses that will occur and correct the situation in the shortest timeframe. Also these classifications, essentially a ‘good, better, best’ approach are easily understood by IT professionals and don’t add to management complexity.
QoS-controlled Snapshots, replication and clones
Storage services like snapshots, replication and cloning create a lot of redundant data. Each of these creates copies that can look to a traditional caching algorithm like new data objects and trigger a move into cache. But in reality they’re most likely not good candidates for flash storage since they’ll only be used in a recovery process.
These ‘false positives’ can quickly consume available flash, space that’s needed for cache-worthy data. ioControl’s QoS-controlled process recognizes these special data objects. When a copy from a snapshot, replication or clone is made, it’s immediately moved into disk storage.
Storage Swiss Take
Hybrid flash systems offer real benefits to companies, like those in the larger end of the SMB space. They can offer the performance of flash in the easy to implement format of a shared storage array. Their weakness has been predictability. Fusion-io is taking the next step in hybrid system design by integrating impressive QoS functionality that can improve performance, predictability and help maximize flash capacity all while reducing the storage management complexity that often haunts hybrid storage systems.
Fusion-io is not a client of Storage Switzerland