By Jun Alejo
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 (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.
The E-Disk Advantage
BiTMICRO Networks, a leading 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 -60°C to +95°C.
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® 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. Fibre Channel and Ultra Wide SCSI E-Disk solid-state
drives' impressive performance up to 70 MB/s sustained reads,
48 MB/s 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.
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. 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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