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Pushing the envelope in blade server design

Posted: 23 Nov 2004 ?? ?Print Version ?Bookmark and Share

Keywords:cpu? memory? solid-state disks? flash ssd?

Blade server computing is fast transforming the server industry with a host of advantages in terms of design, functionality and total cost of ownership. By separating CPU and memory from other components such as cabling, power supply, network connectivity and cooling systems, blade servers significantly reduce massive enterprise server architectures into highly compact and dense form factor. According to market research company IDC, the blade server market is projected to represent nearly 29 percent of server unit shipments worldwide by the end of 2008.

Although its inherent compact design enhances scalability and ease of use for IT administrators, a blade server poses design challenges with regard to the installation of direct attached storage (DAS) devices. Since several blades already share the same power supply, cooling system and chassis, the most logical thing to do is to utilize a low-power, low-heat and compact hard disk drive. The first thing that comes into one's mind is the 2.5-inch mechanical disk drive, the same disk drives installed in notebook computers. However, for enterprise-wide applications, a better solution exists in the form of solid-state disks (SSDs), in particular flash SSDs.

Flash SSDs are high-performance, rugged plug-and-play storage devices that contain no moving parts. Using flash memory chips for storage, these devices are available in the same industry-standard form factors (2.5-inch, 3.5-inch and PMC) and interfaces (Fiber Channel, SCSI, ATA/IDE) as hard disk drives, but instead use flash memory chips in lieu of rotational magnetic disks to store data. This article seeks to explain and illustrate how flash SSDs stack up against other storage devices in blade server applications.

Flash SSDs vs. DRAM SSDs

One SSD variant in the market today is the DRAM SSD. Used mostly in large, rackmount architectures, this device cannot be considered a viable alternative in blade server storage due to several design limitations. Owing to the volatile nature of DRAM memory, a DRAM SSD requires its own power supply, cooling fan and disk backup for data retention. These components eat up valuable space inside the drive chassis, limiting total storage capacity (less room for memory chips) and form factor (smallest DRAM SSD is 3.5-inch). Consider further its weight, and you'll have a recipe for disaster in embedded systems design.

Flash SSDs vs. HDDs

As mentioned earlier, the most important factor in finding the right DAS for blade servers is its impact on overall system performance and cost effectiveness. In terms of power consumption, mechanical hard disks typically devour around 500mA while flash SSDs consume a mere 50mA. The difference may seem insignificant in small enterprise apps, but for huge data farms, the cost savings become apparent. This further enhances the blade server's advantage over proprietary systems with regard to operational costs.

The reliable performance of mechanical disk drives can only be ensured if these drives operate within specified temperature ranges. As drive manufacturers introduce newer models featuring spindle speeds as high as 15,000 RPM, cooling has emerged as a major issue. In fact, some suppliers are providing a dedicated cooling fan or fan/heatsink combos for optimum high-speed drive performance. Unfortunately, the cooling systems of blade servers are shared, and there's no room for these add-ons.

Rugged capabilities

Most blade server vendors are searching for more efficient means of cooling densely packed blades. Hewlett Packard's "dynamic smart cooling" initiative seeks to control heat by focusing cooling on areas identified as "hot spots." For its part, IBM is working on liquid-cooled heat sinks for server processors and water-cooled cabinets. However, these ideas are still under development and are not available now.

Unlike an HDD, a flash SSD generates minimal heat since it has no moving parts, and users can expect the same degree of high-level performance in a wider operating temperature range. These rugged features make flash SSD the most suitable storage platform for Level 3 NEBS-compliant servers. NEBS (Network Equipment Building System) refer to a set of standards established by Bellcore (now known as Telcordia) to determine electromagnetic compatibility, thermal robustness, fire resistance, earthquake and office vibration resistance, and transportation/handling durability of telecom equipment. Telecom carriers deploy equipment to remote locations with unpredictable operating conditions, and NEBS allows them to identify equipment that can provide a high degree of reliability and safety to their network.

The E-Disk advantage

Bitmicro Networks Inc., a player in the flash SSD arena, successfully penetrated the military/industrial markets with its ruggedized E-Disk flash SSDs. These models are guaranteed to operate in extreme temperatures, from -60C to +95C. Other environmental specs are likewise impressive, up to 150Gs of operating vibration and up to 1,000Gs of operating shock, making enterprise and carrier class applications a breeze.

One variant is the E-Disk PCI Mezzanine Card (PMC)-based plug-in flash SSD module. Suitable for blade servers (with PMC slot) that require a reliable, direct attached storage device, it features horizontal connectors that allow parallel fit onto a blade, giving plug-and-play advantages to system administrators. The E-Disk(r) PMC can also be used as a boot and/or storage device for carrier boards such as CompactPCI, VME and MultiBus, and almost any other type of single board computer.

In the enterprise arena, the rising deployment of business intelligence, OLTP (online transaction processing), decision support systems and other transaction-intensive applications place a premium on rapid information transfer, access and retrieval. Fiber Channel and Ultra Wide SCSI E-Disk solid-state drives' impressive performance up to 70MBps sustained reads, 48MBps sustained writes and 12,500 IOPS make them ideal for applications that exhibit grueling, rapid-fire data access brought forth in transactional and high storage bandwidth environments.

At present, blade servers utilize DAS mainly for system boot and application storage, with a Fiber Channel interface designed into the server to allow for a separate SAN connection. Flash SSDs can help improve, not impede, system performance with faster access times, high I/O rates and solid-state durability. Consider other factors such as hot swappability and ease of deployment, flash SSD is certainly an ideal DAS solution for blade servers.

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