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What is Enterprise Storage?

by Hu Yoshida on Aug 26, 2009

The term enterprise storage is thrown around as though it is a well understood term. Every storage vendor claims to have enterprise storage. When we turn to wikipedia for a definition of enterprise storage we find it is very general. It says:

In computing, an enterprise storage is the computer storage designed for large-scale, high-technology environments of the modern enterprises. When comparing to the consumer storage, it has higher scalability, higher reliability, better fault tolerance, and much higher initial price.

I contend that this is a description of commercial storage and not enterprise storage. Only a few storage vendors provide true enterprise class storage. So what do I mean by enterprise storage?

I go back to the early days of computing when IBM 360 mainframes were developed to run multiple virtual systems or MVS. This was the original VM computer, running applications in multiple partitions and driving I/O over special processors called channels. This required a storage system that could support multiple high speed channel interfaces accessing a shared volume. At first the sharing was done by reserve/release commands at the spindle level, but eventually the spindles were virtualized behind a cache and the sharing was managed in the cache tables. This cache architecture enabled multiple storage ports to access one image of a volume in a cache that was shared across all the ports. This ensured high availability since ports could fail or be taken down for maintenance without loss of access to the data through other ports.

Storage ports are driven by processors, and processors on the front were used to drive the channels while processors on the back drove access to the disk and did the RAID calculations. Other processors were added to drive replication. This multiprocessor, shared cache, architecture, provided a storage system that was highly available and highly scalable in performance and capacity. This is the type of architecture that I call enterprise. Today these enterprise systems support open systems as well as mainframes.

The other type of storage is what I call midrange or modular storage. It was designed for direct attach to workstations. Originally they had one processor or controller and supported 15 SCSI targets or Logical Unit Numbers (LUNS). Eventually cache was added and another controller was added for fail over. The cache in the two controllers were separate and so LUNs had to be assigned to one controller or the other to avoid the ping pong effect where a cache image would be loaded in one cache then loaded into the other cache before the first cache image could be accessed. These controllers also had to do the RAID calculations and manage access to the back end disks. If replication was added, these controllers also had to take on that workload.  While midrange systems are not as costly as enterprise systems they are limited in availability and scalability.

Recently new storage systems have been developed which cluster multiple modular systems together, but they do not have the same availability and scalability which comes from the multi-processor, shared cache architecture or an enterprise storage system.

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Comments (3 )

Barry Whyte on 27 Aug 2009 at 1:30 pm

Au contraire Hu. Your final comment couldn’t be further from the truth.

Clustering modular solutions can provide greater reliability of said modular solutions so they match and even surpass traditional monolithic boxes, and they can easily scale out much further than a single scale-up box.

Enrico Signoretti on 28 Aug 2009 at 12:47 am

Hu, i agree with Barry.
New modular (standard hardware) storage can be more scalable,available and rich of features than monolithic systems. Indeed it’s difficult for me to categorize enterprise storage and modular storage but we can add other categories, One of this can be Enterprise Midrange (or modular) storage: http://blogs.cinetica.it/cinetica/2009/08/28/one-size-doesnt-fits-all/.

Enrico

Robert on 28 Aug 2009 at 9:07 pm

I agree with Barry and Enrico. Companies like 3PAR have clusters of controllers which scale very well, and even beat HDS USP in SPC-1 benchmarks, yet cost far, far less.

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