From DAS/NAS/SAN to 'utility-class storage'

A new class of storage system is on the horizon, and it may eliminate the drawbacks associated with direct-attached storage, network-attached storage, and storage area networks.


Direct-attached storage (DAS) is still the dominant method of host-storage connectivity. That will change rapidly due to the increased popularity of networked storage, but the Enterprise Storage Group estimates that more than 80% of all data-center storage is still DAS-based.

Steve Duplessie
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However, DAS is difficult to manage and is usually the most expensive host-storage connectivity method because it does not provide economies of scale (it's a one-to-one relationship). Those shortcomings have led to network-attached storage (NAS) and storage area networks (SANs).

NAS provides file serving (typically NFS and CIFS), or the ability to have Ethernet-networked users view logical drives as though they were local, even though the drives are not directly attached to their systems. NAS provides file-based resource sharing and has become popular because it provides economies of scale (large numbers of users can share a single NAS device) and significantly improved manageability and ease of use.

A SAN provides storage networking for block-level devices, as opposed to the file-level approach of NAS.

SANs are still associated with Fibre Channel, because that is the dominant medium used to create a block-data network. SAN users gain economies of scale by making centralized storage assets available to multiple servers, and consolidation simplifies management relative to DAS.

More recently, NAS and SAN have been lumped together as "networked storage," because with emerging technologies, the traditional definitions of NAS and SAN may no longer apply.

A networked storage environment can handle either file- or block-level I/O. Traditionally, files were only delivered via Ethernet, and blocks were only delivered via SCSI or Fibre Channel, for example. Today, however, with the advent of iSCSI, blocks can be delivered via Ethernet. Files can now also be transported over Fibre Channel, and there are new technologies that allow non-storage IP traffic to be carried over low-latency Fibre Channel.

In short, networked storage, which can deliver data at either the block or file level, is a network of servers and storage devices connected via one or more media.

Next-generation storage will allow for effectively unlimited online, real-time scalability of capacity, bandwidth, and processing. Next-generation storage systems will also provide a single, unified view of the entire environment, assuming that is what the user requires. For example, if the storage system were a file server, it would be able to present a single file system view regardless of how big or small the unit was. It would also provide a single management image, irrespective of the actual components that make up the array(s).

With next-generation storage systems, there will probably be a sub-segment we're calling "utility-class storage," which will offer all of the aforementioned features, in addition to the following:

  • The ability to securely provision a single virtual entity to different "clients"-either independent lines of business within a single organization, or different customers as in the case of service providers.
  • The system will be completely fault- tolerant-or "carrier class"-whereby no component failure, including software, will render the system inaccessible. Maintenance of both hardware and software will be able to occur online and in real time, and microcode roll-backs will be possible without interruption.
  • Quality of Service. The system must be able to guarantee capacity/performance of each provisioned segment. For example, if the finance line of business is deemed more important than marketing, the system should always guarantee response times to the finance department regardless of the load that marketing generates. As such, service providers will be able to guarantee external service level agreements.
  • Accounting. Not a new feature, but the new class of storage system must be able to accurately account for who is using what resources and when.

The utility-class storage sector will also have additional differentiating features among competitors, but all vendors should be able to offer those base-level functions.

Players to watch

In addition to watching well-known players in the DAS/NAS/SAN markets, keep an eye on vendors such as Broadband Storage, ExaNet, Ikadega, LeftHand Networks, Maximum Throughput, Storage Computer, and Tricord.

Examples of new players in the utility-class storage market may include vendors such as Cereva, Panasas, YottaYotta, Zam beel, and 3ParData.

In the near future, you won't buy DAS, NAS, or SAN. Most vendors will have next-generation capabilities, which means everyone will benefit. IT shops will become more scalable than ever, data will become more available, and the overall management burden will be dramatically reduced so that users will spend their time managing "information" instead of storage assets and devices.

Steve Duplessie is an analyst with the Enterprise Storage Group (www.enterprisestoragegroup.com) in Milford, MA.

This article was originally published on December 01, 2001