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IBM Midrange System Storage Hardware Guide
SSD technology
Solid State Drives are built mainly from flash memory and augmented with Dynamic Random
Access Memory (DRAM) along with a sophisticated internal controller. Flash memory based
on the NAND (the logical “Not And” operation) has been available for nearly two decades, and
is used in several high-volume consumer electronics applications, including cell phones,
PDAs, and MP3 players. Flash memory is non-volatile (it retains data without a power
source), involves no mechanical parts, and can be manufactured as standard components in
high volume.
Current flash technology manipulates a charge on the floating gate of specially designed
transistors to allow representation of two (voltage) states, which translates to a single bit per
cell, and is called single layer cell (SLC). SLC NAND-based flash has been dropping in price
faster than DRAM and HDDs, and now sits between them in a price range approximately
twenty to thirty times more expensive than HDDs but up to ten times cheaper than DRAM. At
ten times the price and one hundred times the performance, the value proposition is very
compelling for high IOPS applications. This explains why the technology has been around for
some time but is just now being introduced in storage solutions, including the DS5000 series.
The flash technology is still evolving and we can expect to see a multiple layer cell or MLC in
the future. MLC is designed to allow a more precise amount of charge on the floating gate of
the transistor to represent four different states, so translating to two bits of information per
cell. This higher density per cell and the potential to store three or more bits of information per
cell provides for continuing cost improvement in the coming years. If MLC is successful, flash
memory could reach down to only two to three times the price of high-performance HDDs (FC
or SAS 15K RPM) in the foreseeable future, close enough to drive a significant substitution
rate of low-capacity/high-performance HDDs.
Solid State Drives in tiered storage
Many storage environments have grown to support a diversity of needs and evolved into
disparate technologies that have lead to storage sprawl. In a large-scale storage
infrastructure, this yields a sub-optimal storage design that can be improved with a focus on
data access characteristics analysis and management.
Tiered storage is an approach of utilizing different types of storage throughout the storage
infrastructure. It is a mix of higher performing and higher cost storage with lower performing
and lower cost storage and placing data accordingly based on specific characteristics, such
as performance needs, age, and importance of data availability.
Содержание System Storage DS4000
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