Although HA features were planned for the first XcelaSAN model in Sept. 2009, further testing showed it didn't work to optimal standards with devices from Compellent/Dell, Hewlett-Packard, IBM and LSI. Instead, Dataram began shipping a single unit of the XcelaSAN to customers and spent more than a year redeveloping the high-availability function to make it more bulletproof, said Jason Caulkins, Dataram's chief technologist.
"We had expected to ship [the first XcelaSAN with HA], but the HA portion of the product wasn't meeting our standards," Caulkins said. "We needed to do more work on the interoperability, especially with multiple storage vendors that run simultaneously either in a heterogeneous or homogeneous environment. That took a lot of work. About 90% of our customers have been patiently waiting for HA."
The XcelaSAN Model 100 is essentially the same cache appliance launched in 2009 with software improvements. The upgraded version includes active-active high availability, support for mirrored RAID, hot-swappable components and UPS protection from a power failure. The Model 100 also includes performance monitoring and statistics reporting to assist with SAN performance planning, and an enhanced graphical user interface (GUI) for easier configuration and management.
The XcelaSAN uses flash and DRAM memory to cache blocks for improved performance in Fibre Channel (FC) SANs. It can front any disk array without requiring changes to storage or server environments. The appliance sits between an FC and storage array. It automatically brings the most frequently used blocks of data in a Fibre Channel SAN into DRAM first, and then into NAND to speed performance.
Unlike disk array-based solid-state drives, the XcelaSAN isn't intended to be persistent storage – it moves data to back-end disk. It comes in a 2U network configuration and holds 128 GB of RAM cache and 360 GB of flash. Each appliance costs $65,000, and the appliances are sold in pairs for high availability. Dataram also claims the device can perform at 450,000 IOPs or 3 GBps throughput.
"It automatically comes with flash and DRAM in only one layer of the cache," Caulkins said. "The user can decide which LUNs to cache."
Dataram claims XcelaSAN is the only product on the market that can do high availability in a cache appliance in heterogeneous and homogeneous data centers. Caulkins said the inclusion of flash and DRAM solid-state memory gives customers the best of both worlds. DRAM is fast but expensive and more volatile than flash, and is impervious to being worn out. Flash is cheaper and slower than DRAM but not is volatile.
"What is primarily used these days is flash," Caulkins said. "The more sophisticated the controllers are, the better the flash works. We use both because when there are hundreds and hundreds of thousands of I/Os, DRAM fits that bill while Flash has higher capacity, lower costs and it's non-volatile."
Jim Handy, an analyst at Objective Analysis, said what makes Dataram's flash and DRAM cache appliance unique is that the solid-state disk and cache management comes in one box. "Typically, what you will find, you buy the SSD and you buy the cache software as different components," Handy said. "The easiest thing the XcelaSAN box lets you do is you can plug it in and it just starts to work. You don't have to install any software or anything."
Handy said the company that comes to market first with a cache appliance with high availability will have a firmer foothold in this space. "The first to market will have an easier time entering than any follow-on," he said. "It's not easy for an IT manager to qualify, so if they qualify one, they won't want to spend the time to qualify a second time."
Another thing that helps Dataram stand out is that it handles block data to accelerate SANs instead of delivering a file caching device for NAS such as Alacritech Inc., Avere Systems Inc. and Violin Memory Inc. have done.
"We're considering that [file caching]," Dataram's Caulkins said, "but block-level caching is a more difficult problem to solve."