22-06-2012, 01:40 PM
Introducing Solid State Drives
Solid State Drives overview
Besides an ever increasing demand for more storage capacity, many businesses constantly
require faster storage performance for their high-end, business critical applications.
The hard disk drive technology has improved dramatically over the years, sustaining more
IOPS and increased throughput while providing higher storage density at a lower price.
However, because of its moving and spinning parts, there are inherent physical limitations to
the response times (access time and latency) that an HDD can achieve.
These limitations and the continuing demand for better response times and more throughput
have created the need for a different storage technology that avoids seeks and rotational
delays. This technology, known as Solid State Drives, can provide access times measured in
microseconds.
Solid State Drives use semiconductor devices (solid state memory) to store data and have no
moving parts. SSDs are in fact not new and have existed for a while. They were initially based
on Dynamic random access memory (DRAM) and often referred to as RAM-disks. Although
they had very good performance, they were also extremely expensive and most businesses
could not justify the cost.
SSD endurance
The life of the flash is limited by the number of write/erase operations that can be performed
on the flash. To extend the lifetime of the drive and to ensure integrity of the data on the drive,
SSDs as used in the DS8000 have built-in dynamic/static Wear-Leveling and Bad-Block
mapping algorithms. This is further complemented by Over-Provisioning and Error Detection
Code / Error Correction Code algorithms to ensure data reliability.
These algorithms are implemented in various electronic components of the drive as
functionally depicted in Figure 4. The algorithms are set at manufacturing and cannot be
tuned by the user.
DS GUI and DSCLI changes
Creating arrays, ranks, extent pools, and volumes based on SSDs is the same process as
with regular disks. Some minor changes were made to some DS GUI panels and DS CLI
commands output to reflect the presence of SSDs in the system. Next, we provide some
illustrations.
Note, however, that even though the process is unchanged, there are special considerations
and best practices to follow when creating arrays, ranks, and volumes if you want to keep the
benefits of SSDs. These considerations and best practices are discussed in “Considerations
for DS8000 with SSDs” on page 11.