Storage Interfaces

Sort Through The Options To Make The Right Choice
by George Crump

In 2009, the IT professional might feel like he is faced with many different interfaces to choose from for storage connectivity. On the storage infrastructure side, there is 4Gb Fibre Channel moving to 8Gb Fibre Channel, the option of FCoE (Fibre Channel over Ethernet), and 1Gb iSCSI moving to 10Gb iSCSI. On the storage component side, there is SAS, Fibre, SATA, and even SSD. Each of these options has a viable use in the data center, and working through the options is not as difficult as it appears.

Infrastructure

Paul Vogt, senior director of product management at Xyratex (www.xyratex.com), advises that once you decide you need a SAN or upgrade to a new one, don’t compare performance numbers of the different options: “The protocols are too different; you have to characterize the performance testing with your workload.”

“Also, don’t rule out Fibre Channel just because you have heard that iSCSI is easier,” says Brocade’s Mario Blandini, director of data center infrastructure product marketing (www.brocade.com). Blandini notes that the Fibre Channel of today is significantly easier than the Fibre Channel at the beginning of the decade and that it has become a much easier plug-and-play solution.

Vogt believes that 8Gb Fibre Channel is ready now for most customers, even first-time SAN buyers: “It is the natural upgrade for a current SAN, and the added bandwidth is ideal for IT staffs rolling out their server virtualization projects.” Brocade’s Blandini echoes that sentiment, saying, “Many customers are tempted to start with iSCSI because of perceived ease of use; the challenge is that in virtualized server environments, you quickly begin to push the limits of today’s iSCSI, and the steps needed to scale performance can make the implementation very complex. 8Gb Fibre Channel starts out with plenty of performance and adding to that performance is straightforward.”

FCoE is a 10GbE-based protocol and is positioned to take advantage of both Fibre and IP infrastructures. While FCoE is capturing a lot of attention right now and companies are shipping FCoE HBAs, Vogt believes that because the standard has not yet been ratified, most users will likely wait until mid-2010 before implementing the option. He notes, “Despite that, a Fibre Channel-based protocol, like 8Gb, will have a built-in migration path when FCoE use becomes more commonplace.”

Not to be forgotten is iSCSI. “iSCSI is an ideal protocol for the small to medium-sized enterprise, and now that 10Gb iSCSI is available, the usability is broadening to larger enterprises,” says Condre Senior Storage Engineer Harry Montanye (952/294-4900; www.condrestorage.com).

SCSI is viewed as the affordable alternative to Fibre Channel, and often, in reality, it is. With the improvements in Fibre Channel’s implementation and day-to-day operations, the iSCSI vs. Fibre Channel decision is no longer an issue of ease of use. The decision points now are cost, reliability, and scalability.

“Fibre Channel has proven itself to be more resilient and more scalable than iSCSI vs. iSCSI’s cost advantages, and as those environments begin to scale, much of the cost advantages go away,” concludes Blandini.

Storage Components

2009 will also see change at the storage component level, where the interface choice of Fibre Channel and SATA has been the standard for a few years. “2009 will be the year that we see a dramatic movement to SAS-based disk drives and a decrease in the use of Fibre Channel disk drives,” says Vogt. Montanye agrees, saying, “SAS drives will be the majority of drives used in new storage array purchases, and Fibre Channel drives will be primarily sold to existing users that are not ready to upgrade.”

Compared to SATA drives, SAS is a more enterprise-class drive with a deeper queue depth and the provision for dual-ported drives. The deeper queue depth will improve performance and reduce drive latency. Dual-ported drives will allow for two storage controllers to have direct access to the drives for better failover. In Montanye’s experience, “While SATA drives can simulate this by the use of a path multiplexer, the dollar cost in using a multiplexer can make SATA drives more expensive than the SAS drives, and [in] removing the multiplexer, you eliminate a point of failure.”

“Another advantage to SAS is that its drive connector is interchangeable with SATA,” says Vogt, which he says further lowers cost and system complexity. Vogt also believes that we will begin to see a more rapid transition from 3.5-inch to 2.5-inch drives, based on the new SAS II-based drives. He notes, “This will allow for greater density per cubic inch.”

Storage Decisions

Options are almost always good for the users. Options let users implement a solution based on what they need as opposed to settling for what is available. The problem with choices is that they have to be analyzed and decided upon. The interface decision is largely dependent on what is currently installed and what the IT staff is already comfortable with. If there is already a Fibre Channel SAN in place, staying on that path and migrating to 8Gb FC will likely have an immediate benefit. It would also position the company to take advantage of FCoE when the time comes (if it makes sense in the environment).

Similar is iSCSI: As more systems support iSCSI and provide tools to take advantage of the additional bandwidth, the obvious path of least resistance is to stay with it if it’s the current installation. That said, if there is a need to upgrade, especially if performance is a concern, Fibre Channel should be considered, as well.

The drive mechanisms will, for the most part, take care of themselves. The move to SAS will be part of the normal progression as new storage systems are purchased, and SATA will continue to be the option for the lower-cost tier of storage.

“Flexibility [is] a key feature when selecting your host bus adapter, storage infrastructure, and storage system vendor. Make sure that these providers have the ability to adapt to and interface with emerging standards as they come to market,” concludes Vogt.

It is difficult to know you are picking the right interface. Not only is market acceptance out of your control, but it is also hard to determine what will change internally in your business. The ability to adapt and be flexible is critical.