|RAM SSDs versus flash SSDs? - (aspects of
asymmetries in SSD
Nowadays over 97% of high speed enterprise SSD
capacity is flash memory
The original popular classic article below (which had
contributions from 10 of the leading SSD companies at the time) was
August 2007 at
a time when the enterprise rackmount SSD market was still dominated by
RAM SSDs and there were
many questions about how the market was going to change.
To put this
article into context - with the benefits of 20 20 hindsight.
It was 2
years before SandForce
emerged from stealth mode and reset the 2.5" SSD market.
was the same month that the 1st enterprise rackmount array of flash SSDs
appeared from EasyCo
with a flash management scheme which reduced
SSDs and boosted throughput. In those days - you could burn out most
notebook SSDs in a few months if you placed them into a high IOPs system.
Converting unreliable flash into
remains a design challenge today - because
flash is getting
intrinsically worse as geometries shrink - while markets demand increasing
It was the month before
PCIe-SSD shipped. (It was great on performance - but still didn't include all of
tolerance features which were introduced in later models.)
the month before Texas
Memory Systems launched the
RamSan-500 - a 2TB flash
SSD rackmount with 100K / 10K R/W IOPS. (Symmetric
performance in flash SSDs came a year later in 2008.
advances in flash SSDs - and their market dominance today (in
2012 - year of the
enterprise SSD goldrush) there are still niche roles for
RAM SSDs in very low
latency applications. And there are good reasons why RAM SSDs will remain
1 of the 7 SSD types
in the pure SSD datacenter market of the future too.
conceptual comparisons in the article below - are still valid. But the numbers
RAM SSDs versus
Flash SSDs - which
is Best? - War for the datacenter core10 leading SSD experts discuss
the state of the market - intro by Zsolt Kerekes,
editor (August 2007)
New product architectures have been
closing the performance gap between
flash based SSDs.
flash technology and
media management controllers have blown away the
limitations which made earlier generations of flash SSDs unsuitable for
datacenter applications (regardless of speed).
There is no single "right
answer" to the question - which technology is best. It depends on the
business application and the performance / cost trade offs of reaching
higher server performance.
Revenues for companies in both SSD market
segments (RAM and flash) have been growing fast in recent years. That may
change for individual companies due to lower average selling prices and
competitive alternatives. Lower ASPs will come from falling memory prices
(over the long term) and shorter term from aggressive competition from new
SSD market entrants who want to buy market share. Despite the inevitable
shakeout of many SSD oems - I expect the
number of SSD
vendors to continue growing for the forseeable futures and overall revenue
for both SSD technology segments to continue high double digit growth.
market opportunity represented by the enterprise server
SSD market will be
worth billions of dollars.
Which is best for you? Where is the
I asked leading companies to contribute to this article.
This is what they said.
|Since this article was published - other
ways of looking at the RAM to flash question in SSD apps which are discussed
in other articles are:-
Channel SSDs - these are low latency flash SSDs in a DRAM form factor -
which transfer data via the DRAM channel
- hybrid DIMMs
- these are RAM modules - which back up their temporary data to and on board
flash SSD when the power fails
|In August 2007
Violin Memory launched
the world's fastest 2U SSD and the densest SSD using RAM..|
It was the
first oem to publicly announce that it is developing SSD products with both
|DRAM vs. Flash SSDs|
Perspective from Morgan Littlewood, VP Marketing and Business Development at
It seems unlikely that a single technology will ever
excel across all key dimensions of a storage system, including performance,
capacity and price. The obvious analogy is that while the world's goods are
transported via planes, trucks, trains and ships, each of these markets
continues to grow as trade increases. Performance, capacity and price are also
important attributes of a transport system.
Each core technology has its own limitations. Extracting more IOPS
from disks is increasingly difficult and, hence, disk developments focus on
capacity and bandwidth enhancements. Flash developments focus on capacity and
cost effectiveness, but as a result, performance and reliability are being
negatively impacted. DRAM developments focus on cost and performance
improvements, but are constrained by reliability requirements.
The table below of storage technologies illustrates the unique
attributes of each technology.
Capacity hard disks have a cost/GB
which is significantly better than solid state.
Flash SSDs are very
well suited to read-only applications (and mobility applications).
SSDs have costs per IOPS which are much better than Performance hard disks or
The success of solid state will undoubtedly have most
impact on the performance HDD market.
|Table of Storage Technologies and Key
Metrics - source Violin Memory|
||Cost / IOPs ($)
||Cost / GB ($)|
|Flash SSDs (read only)
Metrics are all normalized as typical rackmount system statistics per U
of height (1.75")
2 - Latency and IOPs estimates assume same
numbers of random reads and writes
3 - Latency and IOPs estimates
assume 4K block sizes
||Within a single Enterprise,
there may be thousands of applications and each of these has its own
performance, cost and capacity issues. Even a common software application (e.g.,
database) can have a wide variety of requirements depending on the size of the
databases, their update rates and the rates and complexity of queries the users
require. Solid state solutions must be able to scale to cover this wide range of
The scalability (capacity, density and performance) of
solid state solutions will determine the size of the market opportunity.
Improved density has the secondary effect of driving down both capital costs and
the operating costs associated with power and cooling. Scalable memory
solutions increase the affordability of the technology to a wider range of
applications and will drive market growth.
DRAM and Flash technologies will co-exist with disk systems and
address the performance and reliability constraints of rotational media. The
unanswered question is: "How will each of these technologies best be used?"
Is Disk emulation the only solution? Why connect to DRAM via a slow disk
attachment interface like Fiber Channel? DRAM has read and write latencies so
low that it can be used as an extension of server memory. Flash reduces the need
for duplicate data copies by dramatically accelerating read-only storage. It is
not clear whether emulating the 4K blocks of hard disks is the most efficient
long term use of solid state technologies.
Violin has designed memory appliances to maximize the technical
benefits of DRAM and Flash technologies either separately or in combination.
DRAM and Flash are installed as high-density plug-in modules. Both disk
emulation and other APIs are supported as configuration options. The objective
is to enable the enterprise with optimal solutions that meet their specific
needs, for a broad range of applications.
In summary, "Solid State Drives" is too limiting a term for
the market segment. Emulating a spinning disk is a not a great aspiration for
solid state technologies, which are radically higher performing. Then again, car
engines are still measured in horse power!
|Solid Data Systems has 14
years experience supplying RAM
SSDs for enterprise speedups. In 2007 they joined the terabyte SSD club and
announced lower price / capacity products.|
|Hard / Flash
/ RAM Disk Performance in Databases|
by Wade Tuma, founder and
CEO of Solid Data Systems
Database transactions are by nature random
and usually come with small block sizes. This
paper analyzes and tabulates cost and performance tradeoffs between
state disks and DRAM-based
It discusses considerations in choosing the right
technology and provides a viewpoint on performance comparison using
industry-standard benchmarks and handy graphical guides for estimating read and
write database performance improvements.
Technologies shipped the industry's first
compatible SSD in April 2005. They also make parallel SCSI and FC models. That
gives them a unique insight into a wide range of enterprise customer speedup
|"RAM versus Flash SSDs
- which is Best?"|
by Tomas Havrda, Solid Access Technologies
vs. SSD, Flash SSD vs. RAM SSD, RAM SSD vs. Ultra fast RAM SSD, mice vs. frogs
whatever it takes to build on the unquestionable excitement surrounding SSD in
2007, I'm for it.
Regardless of which type is purchased, every SSD sale helps to
accelerate the SSD solution concept into the mainstream user's mind-set. Flash
SSDs have received a lot of media buzz, and for some customers it is the perfect
solution. However, they simply won't cut it in demanding enterprise environments
because of their limitations relative to write cycles durability, write
performance, connectivity and device leveraging (multipathing), not to mention
multi-bit error correction capability. Fortunately, SSD customers have plenty of
As the producer of the ultra-fast RAM SSD Solid Access USSD 200, we
know that our USSD 200 solution is, for many applications, the most effective
solution. It can process, via just one single FC port, 95,000 IOPS (read
or write, random or sequential) and 55,000 IOPS via a single wide SAS port. For
more than 2 years, it has been the only
All of our customers could have deployed flash SSDs. Why didn't
they? Because a thorough evaluation of their application issues and
potential solutions led them to USSD 200. They did what every customer should do
they paired a specific problem with the right solution.
SSD OEMs naturally showcase the highest IOPS numbers reached with the
shortest data blocks. However, because applications utilizing SSD typically use
4Kb, 8Kb , 16Kb block sizes, the combination of IOPS and data throughput is a
more relevant measure of the overall application performance boost. For example,
absolute IOPS numbers for USSD 200 FC are higher than for SAS, but the USSD 200
SAS offers twice as much data throughput for read or write (almost 800MB/s
sustained via each wide port) than Fibre Channel, making SAS the fastest SSD
connectivity out there. SAS is also the fastest growing; by the end of 2008,
Gartner predicts data storage interface representation of 41.2% SAS, 22.9% FC,
and 7.3% SCSI. On top of that, SAS HBAs cost 4x less than
Assertions of superiority of one technology over another actually
miss the point. The real issue here is transparency. Performance and pricing
data should be clearly and accurately presented to the consumer; then, let the
customer decide which technology best suits their needs. At Solid Access, we
publish both our price list and our benchmarks. Furthermore, if a potential
customer sends us an IOmeter script based on their app patterns, we will run it
on USSD 200 FC, SAS or SCSI and generate a test result report for them.
Potential customers may also test the SSD solution before committing to buy.
In short, we believe that an unambiguous presentation of pricing and
performance data places the customer in the best position to make an informed,
sound decision regarding their SSD needs.
||Are RAM SSDs Threatened by
Enterprise flash SSDs?|
by Jim Handy,
With all the buzz that is surrounding flash-based
enterprise SSDs these days it would be natural to assume that the DRAM SSD's
days are numbered.
Quite the opposite is the case.
Enterprise flash SSDs offer very fast read speeds, but since they are based on
NAND flash they cannot match the speed of a DRAM device. DRAMs have truly
random access, where NAND flash has a relatively long latency before bursting
out data. Although NAND's 25 microsecond latency is 80x as fast as the 2
millisecond average latency of a 15K HDD, it still is over 1,000x slower than
the 20 nanosecond maximum access of a typical DRAM.
DRAMs also have
significantly faster write speeds than those of NAND, and are byte-writeable:
Any byte of the DRAM can be written to at any time at about the same speed as
its read speed. A NAND chip requires an entire 2K-byte page to be written at
any one time, and before that happens, a 256K-byte block must first be erased,
taking up to 10 milliseconds. To this end enterprise-class flash SSDs use a
small DRAM array to accelerate writes.
A flash-based enterprise SSD is really good at accelerating an
enterprise system at a modest price ($5-10,000) with few changes to the system's
software or hardware. The degree of acceleration depends upon the system's
configuration before the SSD was added. Systems that taxed the ingenuity of the
IT team - ones that use RAID or short stroking to coax more bandwidth out of
enterprise-class HDDs - will see the greatest benefit. The less such
techniques are used, the less the flash SSDs will be able to help.
DRAM SSDs have always been for the most extreme cases. If a flash SSD can be
likened to using dynamite, then a DRAM SSD can be compared to a nuclear bomb.
The system is physically larger than a flash SSD, using a rack or cabinet rather
than an HDD's form factor, and the price may be a cool half million or so, but
the cost/benefit tradeoff can be compelling for those few who need everything
While a flash SSD can reduce the number of enterprise HDDs a system
requires, DRAM SSD makers tell us that the addition of one of their systems can
eliminate the need for a ten or more entire servers.
So, are DRAM
SSDs threatened by flash SSDs? Not at all! As a matter of fact DRAM
SSD makers have told us that the heightened awareness of SSDs in general has
brought prospective customers to them who may otherwise have remained aware that
these extraordinary devices exist.
see also:- Jim Handy's article
DRAM Price Projections - for SSD Buyers
|Memoright makes the
industry's fastest shipping 2.5" SSDs (October 2007). They are targeting
the hard disk replacement market - but their products can also be useful in the
server acceleration market.|
|Introducing the Fastest 2.5"
by Jasmine Hong, Sales Manager, Memoright Memoritech
With pricing trends stable /increasing in Nand Flash post the release
of the Apple Iphone, it appears that the concerns over SSD encroachment have
eased and we could see significant SSD penetration in the notebook market over
the next few years. More and more manufacturers have already begun to introduce
SSDs with varying densities and transfer interfaces, while many kinds of Brand
SSD have entered the market in succession. However, there is a big difference
even among similar looking SSDs in the market.
SSD's storage media is generally based on RAM and Flash. Historically
RAM based SSDs were faster than flash based products - but a RAM based SSD is
much expensive than Flash based SSD and is not usable in all the same
applications for example notebooks.
Memoright's SSD is composed of an
independent intellectual property core controller and flash chip.
flash SSD oems use licensed host interface cores which were originally
designed for slower hard disk drives - Editor.)
technology (which also includes balanced multi-channel read/write) enables
their SSD to deliver 100M Bytes/sec sustained read and write transfer rates -
which is the fastest throughput in a currently available 2.5" flash SSD,
while its random access performance is typically 5x faster than a hard disk.
|BiTMICRO Networks has
been a pioneer and evangelist for the use of
flash SSDs in the
In 2004 BiTMICRO shipped the world's first
Ultra320 SCSI flash SSD (a 3.5" unit with 155GB capacity and 68 MB/sec
sustained R/W rate.)
Driven by a strong belief that the enterprise
storage market will go solid state, BiTMICRO promises to launch more
enterprise-class SSDs in the long term.
|DRAM vs. Flash SSDs|
Joanne De Peralta, Marketing Communications, BiTMICRO Networks, Inc.
Among the inherent advantages of Flash SSDs over DRAM are
lower power consumption, higher density in smaller footprints, ruggedness of
solution, security (securErase), non-volatility and price.
As far as applications are concerned, each application would have
different requirements in terms of performance, ruggedness, security, and
footprint. Flash SSDs would inherently be strong in military/industrial apps and
DRAM SSDs may have an edge in enterprise applications due to some performance
advantages. However, DRAM SSDs are really expensive compared to flash SSDs,
which offer significant performance improvements (vs HDDS) that meet the
requirements of business enterprises.
The random I/O performance of DRAM is superior but the device is more
expensive. Flash is way cheaper than DRAM and can also provide better random
performance than HDDs. Price of flash memory is also going down, making flash
SSDs even more palatable to the enterprise market.
as OLTP, databases, would require high random performance and these are the
types of applications that DRAM or flash would be very strong in. However, flash
SSDs gets the plus points with regard to non-volatility (they don't require
batteries for backup), capacity (denser memory chips due to R&D advances)
and form factor (drop-in replacements for HDD).
Attorn for a
contribution to this article because its HyperDrive4 (available in 5.25"
CD drive form factor) stands at the threshold of entry level RAM SSDs.|
August 2007 the company launched a rackmount HyperDrive4, which the company said
(at $250 per gigabyte) was the lowest price per gigabyte for a RAM based solid
|"RAM versus Flash SSDs
- which is Best?"|
by Jan Wels, Attorn
Our RAM SSD
products based on the HyperDrive4 are able to solve various application issues
that were not previously being solved by alternative methods of archival and
retrieval. This is due to the constant available high IOPS and STR regardless of
the setting in which it is applied, be it in web or file servers, databases or
as replacement of in-server memory systems.
There is no other
technology that can match the performance of a RAM SSD, especially in an
environment where there are a significant number of write operations.
Of course for many applications the performance will not be so
critical that the investment cost of a RAM SSD is warranted and a Flash SSD will
offer a good alternative.
For the foreseeable future we see a market where there is room for
both solutions alongside the normal hard disk. With HyperDrive4-array sales and
placements in multi billion dollar corporations around the globe our RAM SSD is
gaining market respect with each installation. The fact that this new product
leads the market from a pricing perspective has not disappointed customers from
a quality, reliability and most importantly performance perspective.
expectations for the fourth quarter of 2007 look good and we expect the
HyperDrive4 to gain further momentum in 2008. Development in the next 2 to 3
years of our RAM SSD's will result in a further increase of the performance and
we expect to reach 1,000,000 IOPS per drive and a STR of 300MB/s.
For the longer term we think that two factors will determine whether or not
there is room in the market for both RAM and Flash SSD's. First if the Flash
SSD's will be able to bridge the performance gap with RAM SSD's, and secondly
the development of the price difference between RAM and Flash memory.
|In August 2007
EasyCo launched its
revolutionary "Managed Flash Technology." |
flash SSDs (but
addressing them in a completely new way) the technology results in system
write performance that is typically 100x faster than the bare solid state
MFT, which is shipping today in Linux servers, changes
the boundaries of flash SSD system performance.
Flash SSD Performance|
by Douglas Dumitru, CTO EasyCo LLC
intro:- Douglas Dumitru has written a
paper which will become the classic reference for systems engineers who want
to understand the dynamics of flash versus hard disk performance running real
It begins by comparing in detail the performance achieved
by commodity flash SSDs for various read / write size blocks to that of high
performance hard drives. The dropoff in overall performance for various ratios
of reads to writes is also documented.
This article also briefly
notes and analyzes the performance of high end RAM SSDs and the fastest
commercially available flash SSDs.
Understanding these real world
constraints, the article leads on to an explanation of EasyCo's patent pending
Managed Flash Technology which delivers random
write performance in a flash SSD array which is almost 500x
the performance of the bare drives running RAID-5. This changes the mapping
scheme in the flash memory dynamically to work around contention caused by block
erases. This revolutionary approach works with commercially available flash
SSDs and is scalable. ...read the
|Conspicuous by its absence from
the first published version of this article, the reason for the company's
reticence on the subject of flash versus RAM SSDs became clear in September 2007
- when Texas Memory
Systems launched the RamSan-500. |
The RamSan-500 is 4U rackmount
flash SSD with 100,000 IOPS sustained random read, 10,000 IOPS sustained
random write and 2G bytes / sec sustainable throughput from fibre-channel hosts
to internal flash storage.
At first glance it looks as if the
RamSan-500 takes a similar approach to flash write management as EasyCo's MFT
(see above) but TMS uses different design decisions - and implements the
process transparently within the hardware of the SSD instead of needing an OS
in the Enterprise|
by Jamon Bowen, Texas Memory Systems
memory is poised to become a major player in datacenter storage systems. It
provides an all electronic method of storing data in silicon, removing the only
component in modern data processing systems that still relies on moving parts in
the data path: the spinning hard disk. Though Flash memory offers some
compelling advantages over disk-based storage, it is not well understood in the
storage industry. This
describes some the properties of Flash memory and then explains how the
RamSan-500, produced by Texas Memory Systems, leverages its strengths and
compensates for its weaknesses to offer the first enterprise ready Flash system.
extract - Write Performance
"The RamSan-500, due to its design, achieves a much higher level
of Flash write performance, making the technology enterprise-ready. The large
battery backed DDR RAM cache is used to buffer write operations (random or
sequential) so host processing can continue after only the cache write. The back
end Flash controller takes the buffered writes and maps them to a new physical
location every time they are written, ensuring that new writes are always
written sequentially to locations in the Flash and thus avoiding the random
write Flash penalty."
2007 was a
Year of Revolutions in the SSD Market.
The snapshot given in this
article is far from the last word on innovation in the "RAM versus Flash
Let's not forget that a general factor which is
increasing the level of random write performance in flash SSDs is increased
parallelization within the SSD itself.
unfortunately was unable to meet our publication deadline) has "bet the
company" on its ability to deliver high capacity, high IOPs flash SSDs with
its Zeus IOPs family. In some applications STEC's products will compete for rack
space with many of the alternative solutions from the vendors above (and
others). On the other hand EasyCo's
MFT (which the company says it is offering to license to other oems) may
work equally well as a speedup - using intrinsically faster disks. That remains
to be seen.
Also let's not forget that in May 2007
MOSAID unveiled its
HyperLink NAND Flash memory architecture which (the company claims) can increase
write performance by 10x using current levels of technology. That could push the
performance of hard disk form factor flash SSDs to new heights.
April 2008 - we published Predicting
Future Flash SSD Performance - a timeline and notes predicting flash SSD
performance upto 2012.
In May 2008 - we published
Calling for an
End to Unrealistic SSD vs HDD IOPs Comparisons
In June 2008 - the
article Is the
SSD Market Recession-Proof? paints a different picture for the RAM and flash
SSD markets. Many oems have told me that greater awareness of SSDs (due to flash
SSD marketing) is making it easier to sell RAM SSDs too.
June 2008 - Solid Access Technologies published a
presentation explaining the advantages of its fast RAM SSDs. Of particular
interest are slide 5 (which lists traditional methods for reducing I/O
bottlenecks) and slide 6 (which uses a mail delivery analogy to position various
types of storage).
In October 2008 -
Solidata published an
article - Flash-based
SSDs vs. DRAM-based SSDs - which points out the similarity of the SSD
market today with the NAS market about 10 years ago - and the difficulties
facing customers. Do they risk more by buying from more expensive old style
vendors? - or from newer companies selling at a lower price?
updates on this subject check the main
articles may also be interesting:-
of bad block management in flash SSDs
Flash Memory vs. Hard
Disks - Which Will Win?
How Bad is - Choosing the
Wrong SSD Supplier?
Using SSDs to Boost
Legacy RAID Performance
SSDs with Gigabyte / S Performance
Hybrid Storage Drives
- winners, losers and maybes
SSDs, tonic medicine and
the next flash / flu pandemic
Flash vs DRAM
Price Projections - for SSD Buyers
War of the Disks: Hard
Disk Drives vs. Flash SSDs
Why Consumers Can Expect
More Flaky Flash SSDs!
Clarifying SSD Pricing -
where does all the money go?
Can you believe the
word "reliability" in a 2.5" SSD ad?
Fast Purge flash SSDs -
when "Rugged SSDs" won't do the job
Calling for an
End to Unrealistic SSD vs HDD IOPS Comparisons
an Introduction to SSD
Data Recovery Concepts and Technologies
the Most Popular
Products on StorageSearch.com - (2007 to 2010)
Legacy versus New
Dynasty - a new way of looking at Enterprise SSDs