| When flash SSDs aren't fast
enough! |
RAM based SSDs are the
original type of
solid state disk and have
been around for
decades.
They rely on batteries to retain data when power is lost. Most
models also include internal
hard disk drives to
which data is saved under battery power, so that data is not lost when the
battery runs down. This hybrid technology means that RAM based SSDs are more
bulky than
flash counterparts
and RAM SSDs are unable to operate in the same range of
hostile environments.
RAM based SSDs are mostly used in enterprise server speedup
applications. The fastest RAM SSDs are faster than the fastest
flash SSDs. But
for many server speedup applications flash SSDs are fast enough.
Unlike
flash SSDs, RAM based SSDs never had restrictions on the number of write
cycles. That made them more popular in enterprise acceleration applications in
the past. But write
endurance problems may be a thing of the past for flash.
Like hard
disks - RAM SSDs have symmetric read/write IOPS. That's another big
difference between
RAM and flash SSDs.
The fastest flash SSDs available in 2009 had
achieved parity between random read and write IOPS.
But that's not how
transaction based applications work. The important differentiator here isrepeat again write
IOPS. If you compare that between RAM and flash based SSDs - the RAM
SSDs are upto 100x faster - even when the datasheets suggest they look
the same.
On the other hand - in some enterprise applications - like
IPTV servers - the random write IOPS rarely repeats in the same memory space
during milli-second timeframes - and in these video server apps - flash really
does perform as well as RAM - and is much cheaper.
Latency figures
quoted by many flash SSD products can also look very similar to those for RAM
SSDs. But low random write latency doesn't mean that the data has actually hit
the flash media yet - as you'll find if you try to read back the data and
rewrite to the same block.
There are also some non volatile memory
products such as
PRAM,
FRAM and RRAM which are replacing flash in industrial applications - and
which already offer 1 to 1 read/write performance. But their capacity is 2
orders of magnitude too low to be of use in server applications.
RAM
SSDs cost about 9x as much as SLC flash SSDs (based on rackmount
pricing data Q4 2009.)
The ideal choice of SSD depends on the specific
server and application environment and cost / benefit analysis.
Not
everyone needs or can afford the
fastest SSDs. Some
environments do. Others don't.
Identifying the right choice of SSD in
the right place is a complex decision - which requires a high degree of
SSD education and
trust in the vendor.
More articles about the problems and solutions
related to accelerating enterprise server apps can be seen on the
SSD ASAPs page. | | |
|
 |
Energy Data Storage
2010
by SMi Group
November
3 - 4, Kensington, London |
This new event
will form a platform for the
energy sector to discuss and compare their
unique digital data storage needs. | | |
