Hu's Blog

While the need for storage continues to increase, there seems to be a trend in the decline of modular storage business for some of the major storage vendors. This may be due to the aging of the traditional modular storage architecture.

This architecture was designed over 20 years ago  for direct attach to open systems storage. For redundancy, it had two active/passive  controllers, meaning one controller actively handled the I/O and RAID processing for a set of LUNs while the other controller was in standby. While the other controller could handle I/O for a separate set of LUN’s, this LUN to controller ownership had to be carefully planned to avoid I/Os from “ping ponging” across the separate controllers trying to find their cached data. Unlike enterprise storage systems where all the controllers are tightly coupled through a common, global  cache, the two controllers have separate caches and only mirror writes to the other cache for write protection in case one of the controllers fail. This simple design makes it less costly to manufacture than enterprise systems with multiple controllers coupled through a large global cache, but it lacks the scalability and advanced functionality of enterprise systems. The modular storage systems are also easy to expand by adding additional drawers of disks into a storage rack and daisy chaining them to the other drawers in the rack.

The AMS 2000 modular storage architecture preserves these benefits of lower cost and ease of expansion while eliminating the performance restrictions and configuration complexities of  active/passive controllers. While the AMS 2000 is still a two controller system with separate caches, the controllers automatically load balance the LUN ownership between controllers. This increases overall performance and simplifies operation by relieving the operator of LUN ownership concerns. Another improvement is the use of point to point, Serial Attached SCSI, for the backend disk attachment in place of FC Arbitrated Loops. This eliminates loop contention,  makes it easier to intermix device types like, Flash, SAS, and SATA, and provides isolation of disk failures for improved availability.

This new generation of modular storage systems is quickly gaining market share while other traditional modular storage systems are in decline. We are pleased that SEPATON announced they will integrate the AMS 2100 into their VTL backup solution. While Hitachi Data Systems is not a reseller of the SEPATON VTL product, their announcement is another proof point for the need for new generation modular storage systems.