SAS for the SMB: A Guide For System Integrators

Author: David Woolf – Senior Technical Staff
University of New Hampshire InterOperability Lab

When it comes to data storage and protection, small and medium businesses (SMBs) often find themselves not knowing where to turn for data storage solutions. They are torn between high-end product offerings intended for large enterprises, or trying to piece together a data storage solution from products intended for home users.

Like a large enterprise, a small or medium business has increasing data storage needs as the business grows. Data is a critical part of any business. Also like a large enterprise, a small business needs scalability, backup, and possibly some form of information life-cycle management (ILM).

In many cases the best solution for these needs is a storage area network (SAN), but SANs are expensive. Although the price for SAN equipment is decreasing, the high cost of the initial investment remains, making it prohibitive for a small business. An SMB does not always have the resources necessary to devote to an IT staff to support its storage needs. SMBs need a storage technology that allows flexibility, ease of use, and a lower total cost of ownership.

SAS is the Solution
The solution is Serial Attached SCSI (SAS) and Serial ATA (SATA). These new drive interconnect technologies provide a beacon on the horizon for small businesses with growing data storage needs, and who are looking for something easy to deploy at low cost. How will these new storage technologies be useful for SMBs? Lets look first at each of the technologies.

SAS has emerged as the replacement for parallel SCSI. With data rates of 3Gbps, and a migration plan to 6 and 12Gbps, SAS is here for the long term. A SAS expander allows up to 16,000 devices to be connected. Although most host bus adapters do not yet support this high theoretical limit, clearly SAS allows for far more devices than a traditional parallel SCSI bus. SAS delivers the same high mean time between failures (MTBF) as parallel SCSI as well as the same command support, making it compatible with existing applications that use SCSI.

Add SATA to the SAS Solution
SATA is a disk drive technology with fewer features, which makes it extremely inexpensive. Current SATA products on the market have data rates of 1.5Gbps with a migration path to 3Gbps. Originally intended as the replacement for parallel ATA, SATA has gained traction as the drive of choice for nearline storage, where high capacity per drive, and low cost, make it attractive for this low-traffic volume environment.

Much has been written about SAS as a replacement for parallel SCSI in the enterprise. Compared to parallel SCSI, SAS offers better scalability, higher performance and greater flexibility. Much has also been written of how SATA will be used by large enterprises as a vehicle for nearline storage and to implement ILM at lower cost.

SATA is a lower cost, lower performance and high capacity solution. SAS is a higher cost, higher availability, higher performance, lower capacity solution and they are compatible in the same SAS infrastructure. An aspect of combining SAS and SATA in the same system, that will be particularly useful to SMBs, is the capability of a SAS system to natively support SATA disk drives. SAS disk drive enclosures will be able to support both SAS and SATA disk drives in the same chassis without any additional configuration or hardware necessary. This capability offers two key benefits for the SMB.

First, using SAS controllers and expanders allows for more complex SATA topologies than would be possible with SATA controllers. Since SATA was designed with the desktop in mind and a desire to keep cost as low as possible, it is not very scalable. Adding more drives to a system therefore requires adding more host ports. This is unattractive in an environment where scalability is needed. However, using SAS host bus adapters and SAS expanders would allow thousands of SAS and SATA drives to be connected to a single SAS controller, thereby taking further advantage of a SATA disk drive’s lower cost.

Second, because of its flexibility, a SAS enclosure can save users money in the long run. A SAS enclosure can be used initially to house high performance SAS drives. Later on, as newer, higher performance enclosures are purchased, the original enclosure still has value for housing lower-cost SATA drives, or a mix of older SAS and SATA drives. Instead of collecting dust, the SAS enclosure is still an extremely useful part of the storage plan, particularly for storing archived data that is rarely accessed, but needs to be retained.

The unique ability of SAS to support two different drive technologies makes it extremely adaptable, including to the needs of an SMB. Instead of worrying about the high cost of implementing a SAN, or trying to piece together low-cost storage to fit their needs, SMBs can take advantage of the flexibility of SAS and build a reliable system to fit their needs—and their budget.

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