Batteries in the data center are problematic. Traditional lead-acid batteries outgas hydrogen (an explosive gas), they can leak acid which can make a real mess of cables and equipment, and they take a lot of space in addition to being pretty heavy. In addition, there are issues with cells drying out, interconnect degradation and thermal runaway problems. Modern Li-Ion batteries are much better, they just occasionally burst into flames.
There are practical considerations as well. Batteries require service. The logistics for 100 arrays and their batteries gets messy very quickly. Since the batteries will not last as long as the array, this scenario may be repeated multiple times during the life of the array. Finally, there might be a problem with local building codes. The National Electric Code® doesn’t seem to support batteries outside the building infrastructure. Not every local jurisdiction uses the National Electric Code, but most do.
Why are batteries needed in flash storage systems? They’re not. They exist as a workaround for poor system design. Flash systems that have always-on data reduction and SSDs are particularly likely to have large amounts of DRAM to process incoming data. In the event of a power outage, the data must be protected in any enterprise class solution. Therefore a DRAM-based design must include batteries to de-stage data from volatile DRAM to non-volatile flash storage.
Violin’s Flash Fabric Architecture™ does not require batteries, by design. Violin storage certainly has some DRAM in the system for our deduplication and other processing needs. The difference is that we also use a small amount of our high-performance Violin Intelligent Memory Module (VIMM) flash to process inbound data, including data reduction. In the event of a power failure there is no compromised data, and no need to use batteries.
Over reliance on DRAM for array functions leads to the need for batteries. By the way, over reliance on DRAM also creates an inconsistent performance profile: you may notice the performance drop when work moves from DRAM to flash. Primary storage needs consistent performance, not latency spikes from over reliance on DRAM.
There is no need to use batteries for all-flash arrays that are well designed. You don’t need to design your data center around battery problems in your arrays. Violin Memory’s all-flash storage arrays don’t need batteries. You don’t either.