Solid-State Disks: Pushing the Envelope in Blade Server Design

Blade server computing is fast transforming thefor these add-ons.
server industry with a host of advantages inRugged Capabilities
terms of design, functionality and total cost ofMost blade server vendors are searching for
ownership. By separating CPU and memory frommore efficient means of cooling densely packed
other components such as cabling, power supply,blades. Hewlett Packard's "dynamic smart cooling"
network connectivity and cooling systems, bladeinitiative seeks to control heat by focusing cooling
servers significantly reduce massive enterpriseon areas identified as "hot spots." For its part, IBM
server architectures into highly compact andis working on liquid-cooled heat sinks for server
dense form factor. According to market researchprocessors and water-cooled cabinets. However,
company IDC, the blade server market isthese ideas are still under development and are
projected to represent nearly 29 percent ofnot available now.
server unit shipments worldwide by the end ofUnlike an HDD, a flash SSD generates minimal
2008.heat since it has no moving parts, and users can
Although its inherent compact design enhancesexpect the same degree of high-level
scalability and ease of use for IT administrators, aperformance in a wider operating temperature
blade server poses design challenges with regardrange. These rugged features make flash SSD
to the installation of direct attached storagethe most suitable storage platform for Level 3
(DAS) devices. Since several blades already shareNEBS-compliant servers. NEBS (Network
the same power supply, cooling system andEquipment Building System) refer to a set of
chassis, the most logical thing to do is to utilize astandards established by Bellcore (now known as
low-power, low-heat and compact hard disk drive.Telcordia) to determine electromagnetic
The first thing that comes into one's mind is thecompatibility, thermal robustness, fire resistance,
2.5-inch mechanical disk drive, the same diskearthquake and office vibration resistance, and
drives installed in notebook computers. However,transportation/handling durability of telecom
for enterprise-wide applications, a better solutionequipment. Telecom carriers deploy equipment to
exists in the form of solid-state disks (SSDs), inremote locations with unpredictable operating
particular flash SSDs.conditions, and NEBS allows them to identify
Flash SSDs are high-performance, ruggedequipment that can provide a high degree of
plug-and-play storage devices that contain noreliability and safety to their network.
moving parts. Using flash memory chips forThe E-Disk Advantage
storage, these devices are available in the sameBiTMICRO Networks, a leading player in the flash
industry-standard form factors (2.5-inch, 3.5-inchSSD arena, successfully penetrated the military
and PMC) and interfaces (Fibre Channel, SCSI,industrial markets with its ruggedized E-Disk flash
ATA/IDE) as hard disk drives, but instead useSSDs. These models are guaranteed to operate in
flash memory chips in lieu of rotational magneticextreme temperatures, from -60°C to
disks to store data. This article seeks to explain+95°C. Other environmental specs are
and illustrate how flash SSDs stack up againstlikewise impressive, up to 150Gs of operating
other storage devices in blade server applications.vibration and up to 1,000Gs of operating shock,
Flash SSDs vs. DRAM SSDsmaking enterprise and carrier class applications a
One SSD variant in the market today is thebreeze.
DRAM SSD. Used mostly in large, rackmountOne variant is the E-Disk PCI Mezzanine Card
architectures, this device cannot be considered a(PMC)-based plug-in flash SSD module. Suitable for
viable alternative in blade server storage due toblade servers (with PMC slot) that require a
several design limitations. Owing to the volatilereliable, direct attached storage device, it features
nature of DRAM memory, a DRAM SSD requireshorizontal connectors that allow parallel fit onto a
its own power supply, cooling fan and disk backupblade, giving plug-and-play advantages to system
for data retention. These components eat upadministrators. The E-Disk(R) PMC can also be
valuable space inside the drive chassis, limiting totalused as a boot and/or storage device for carrier
storage capacity (less room for memory chips)boards such as CompactPCI, VME and MultiBus,
and form factor (smallest DRAM SSD is 3.5-inch).and almost any other type of single board
Consider further its weight, and you'll have acomputer.
recipe for disaster in embedded systems design.In the enterprise arena, the rising deployment of
Flash SSDs vs. HDDsbusiness intelligence, OLTP (online transaction
As mentioned earlier, the most important factorprocessing), decision support systems and other
in finding the right DAS for blade servers is itstransaction-intensive applications place a premium
impact on overall system performance and coston rapid information transfer, access and retrieval.
effectiveness. In terms of power consumption,Fibre Channel and Ultra Wide SCSI E-Disk
mechanical hard disks typically devour aroundsolid-state drives' impressive performance up to
500mA while flash SSDs consume a mere 50mA.70 MB/s sustained reads, 48 MB/s sustained
The difference may seem insignificant in smallwrites and 12,500 IOPS make them ideal for
enterprise apps, but for huge data farms, theapplications that exhibit grueling, rapid-fire data
cost savings become apparent. This furtheraccess brought forth in transactional and high
enhances the blade server's advantage overstorage bandwidth environments.
proprietary systems with regard to operationalConclusion
costs.At present, blade servers utilize DAS mainly for
The reliable performance of mechanical disk drivessystem boot and application storage, with a Fibre
can only be ensured if these drives operate withinChannel interface designed into the server to
specified temperature ranges. As driveallow for a separate SAN connection. Flash SSDs
manufacturers introduce newer models featuringcan help improve, not impede, system
spindle speeds as high as 15,000 RPM, cooling hasperformance with faster access times, high I/O
emerged as a major issue. In fact, some suppliersrates and solid-state durability. Consider other
are providing a dedicated cooling fan or fanfactors such as hot swappability and ease of
heatsink combos for optimum high-speed drivedeployment, flash SSD is certainly an ideal DAS
performance. Unfortunately, the cooling systemssolution for blade servers.
of blade servers are shared, and there's no room