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  Using Solid-State Disks for Blade Servers
 
 

Solid-State Disks: Pushing the Envelope in Blade Server Design
Written By: Jun Alejo
Edited By: Agi

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, there may be a better solution 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 (Fibre 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.

Conclusion

At present, blade servers utilize DAS mainly for system boot and application storage, with a Fibre 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. Considering other factors such as hot swappability and ease of deployment, flash SSD may be an ideal DAS solution for blade servers.

Jun Alejo is a Marcom Specialist at BiTMICRO Networks, one of the leading companies in the flash SSD arena. You can reach him at jalejo@bitmicro.com.

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