Page 45 - Coal Quality Testing

and performance. Flash can not be the important properties of NVRAM (fast,
viewed as a replacement for existing persistent writes), while avoiding the
storage but rather a means to enhance downsides (cost, size, battery power). It is
it. Conventional storage systems mix possible to build a flash based device that
dynamic memory (DRAM) and hard drives, can service write operations very quickly
flash is interesting because it falls in a by inserting a DRAM write cache and then
sweet spot between those components treating that write cache as non-volatile
for both cost and performance in that by adding a super capacitor to provide
flash is significantly faster than disc. the necessary power to flush outstanding
data in the DRAM to flash in the case of
power loss.
Properties of Flash Storage
Memory Many applications such as data bases
can use a dedicated log device as a way
Flash has two distinct categories: NAND of improve. The performance of write
and NOR that refer to the way the flash operation; for these applications, such a
cells are arranged. NOR flash allows device can be dropped in easily. To bring
for random access and is best suited the benefits of flash log device to
for random access memory, while primary storage, and therefore to
NAND must be treated as blocks and wide array of applications, one
ideal for persistent storage. The rest of needs similar functionality
this article examines only NAND flash, in a general-purpose file
the cheaper and more common their system.
other types: single – level cell (SLC)
and multilevel cell (MLC). SLC stores a
single binary value in each memory cell.
The binary value in distinguished by
two threshold voltages. MLC supports
four or, recently, eight distinct values
per memory cell corresponding to two
or three bits of storage. Because of its
improved longevity and performance,
the conventional wisdom is that SLC
is best suited for enterprise solution.
While completely accurate comparisons The
between flash, DRAM and hard drives Impact of Flash
are difficult because of differences
in capacity and interfaces, it is fair to By combining the use of flash as an
say that flash consumes significantly intent-log to reduce write latency with
less power than those other systems flash as a cache to reduce read latency,
components, especially on per gigabyte we can create a system that performs
basis. Most flash devices are also capable far better and consumes less power
of estimating their own remaining life than other systems of similar cost. It
time so system can anticipate failure and is precisely to construct systems with
take prophylactic actions. flash for caching, DRAM, and cheap discs
designed specifically to achieve the right
balance of cost and performance for any
Flash as a Log Device given workload, with data automatically (To be continued in next issue
handled by the appropriate level of correlating nanotechnology and
Flash memory discs or media is used hierarchy. computer engineering) | w w w . qcin. or g | w w w . qcin. or g
as a stand-in for NVRAM that improves
write performance as a log device. To
that end you need a device that mimics

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