Special Report: Standards Rule: Storage and Servers

If you've shopped for storage and server hardware in the past six months, you've probably noticed some changes in your favorite vendors' offerings. Speed is everything, and the serial revolution is finally making its way to a server near you, with disk and I/O performance you've only dreamed about.

PCI-ExpressThe venerable PCI bus has dominated IT as the system interface of choice for more than a decade. But with upcoming I/O solutions for storage and networking exceeding 10 Gbps--or 1,250 MBps--the PCI-X/133 bus common to most servers doesn't have the bandwidth to handle the load. To pick up the pace, PCI has moved from parallel to serial architecture; the serial-based PCIe (Peripheral Component Interconnect-Express) interface ushers in a new level of high-speed I/O on the system board.

PCIe ruled as the video interface in high-performance desktop systems, and now server manufacturers are finally beginning to offer PCIe options on their newest systems. Unlike PCI-X, PCIe is a dedicated point-to-point interface rather than a shared, parallel bus architecture. It offers lower latency, full duplexing and scalable bandwidth capable of reaching nearly 10 GBps on a single PCIe x16 link. By comparison, the new, parallel PCI-X 2.0 standard offers a 266-Mhz bus speed, and eventually 533 Mhz; but can only support 2.1 GBps and 4.3GBps, respectively, that must be shared by the entire bus.

It's often an either-or proposition, and many vendors still offer their systems in PCI-X with the option to upgrade to PCIe. Perhaps this is in response to the limited availability of enterprise-class PCIe cards, but be aware that all the major card vendors have already announced high-performance network and RAID controllers in PCIe. Even conservative Dell has chosen to fully embrace PCIe as the interface of the future in its new G9 server series. Unless you have an overriding need to support specific legacy PCI-X cards, it's hard to imagine a good reason to purchase servers without PCIe capabilities.

» PCISIG standard, version 1.1

» PCIMGSAS/SATA

One indicator of the high-speed serial interface's success was the overwhelming adoption of SATA (Serial Advanced Technology Architecture) disk drives on the desktop, starting in 2003. The interface reduced cables to a fraction of their previous size, simplified connectivity and offered bandwidth that now reaches 300 MBps.

SAS (Serial Attached SCSI) followed in 2005 as the serial version of the industry-standard parallel SCSI interface. Among the improvements SAS made to SCSI were smaller cables, hot-swap capabilities, higher bandwidth, full duplexing, high-speed external connectivity, dual-channel capabilities, substantially improved device addressing and the ability to seamlessly use both SAS and SATA drives with the same SAS controller.

SAS and SATA are a marriage made in heaven. Because they share a common backplane interface, both drive types can be mixed and matched. This lets the end user choose between pricier, high-performance SAS drives and inexpensive, high-capacity SATA drives in the same enclosure to suit their application and budget. Practically every manufacturer offers SAS options in their newest server platforms, and like PCIe, SAS and SATA are destined to be the long-term replacements for their parallel counterparts.

An interesting side note to the growing popularity of the SAS interface is a renewed interest in the 2.5-inch form-factor enterprise-class drive. Spindle count is everything for high-performance disk applications, and 2.5-inch drives let engineers double the number of spindles in the same amount of space. This option is available from most first-tier server vendors.» SAS: INCITS T10 Committee

» SATA: SATA-IO

» SCSI Trade Association

iSCSI

Internet Small Computer System Interface isn't all that new, but it's getting newfound attention, thanks to 10 Gigabit Ethernet, which may breath life into an also-ran storage platform. Large-scale FC (Fibre Channel) installations have dominated the SAN industry. Even though FC currently enjoys 97 percent market share, Ethernet-based iSCSI SAN storage is whittling away at the competition and is now showing 105 percent annual revenue growth, according to industry analyst IDC.One big difference between FC and iSCSI storage has always been in the network interconnect bandwidth. While iSCSI was limited to a Gigabit Ethernet connection, FC has been running at 2-Gbps and now 4-Gbps speeds. Yes, iSCSI vendors could bond multiple GbE ports to match FC, but the perception remained that FC was faster. Now that 10GbE is becoming a reality, the tables are turned. Vendors backing iSCSI have the potential to leverage the increased bandwidth, along with less expensive SATA disk and cost-effective management technology, to pose a serious challenge to FC.

No one expects FC's domination to end very soon, but Ethernet-based technology has been unquestionably successful wherever it's been applied. A surprising number of IP storage vendors have announced high-performance and cost-effective 10GbE products, and per-port prices are dropping for switches and adapters. Storage is a real sweet spot for 10GbE technology, especially for SMB networked storage. The timing couldn't be better when you consider that SAS/SATA and PCIe offerings are already in place to ensure that there are no bottlenecks in this new world of really, really fast I/O.

» IETF standard, RFC 3720

» SNIA

Steven Hill, an NWC technology editor, can be reached at [email protected].0