I used RAM SSDs (both SCSI based and native backplane bus based)
back in the 1980s to accelerate Oracle on servers but most often in ultrafast
embedded real-time platforms.
And I've been writing about RAM SSDs
in my enterprise
buyers guides for over 20 years. So I've seen this market in many different
phases of its life.
The enterprise SSD market - which used to be
100% RAM based over 10 years ago - is now
overwhelmingly dominated by
flash. You can read a
summary of how this tranformation took place in
the evolution of
enterprise flash - a 10 year history
Reports from SSD vendors
suggest that RAM SSDs and
RAM cache in flash
SSDs probably account for no more than 1 to 2% of all
enterprise SSD capacity.
But RAM SSDs are not entirely dead, in new
architecture design - and will
remain an essential
way to unbottleneck
large clusters of fast flash SSDs.
For example it's a shared
multiported ultrafast RAM replication resource which is at the heart of
A3CUBE's PCIe fabric -
(launched in February 2014) which offers a new way to leverage huge populations
of PCIe SSDs and
Having said that - the ratio of real RAM - even inside
servers - is under attack and likely to shrink due to a new type of flash SSD
- memory channel
SSDs - which you can read more about in the special directory here on
SSDs aren't fast enough!|
|RAM based SSDs are the
original type of
solid state disk and have
been around for
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
and RAM SSDs are unable to operate in the same range of
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.
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.
disks - RAM SSDs have symmetric read/write IOPS. That's another big
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 is repeat 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
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.
are also some non volatile memory products such as
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.
SSDs cost about 3x as much as SLC flash SSDs for similar capacity in FC
SAN rackmount systems - (based on pricing data 2011.)
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.
|how fast can your SSD run
|Editor:- April 20, 2012 - StorageSearch.com today published
a new article which looks at the
11 key symmetries in
SSDs are complex devices and there's a lot of
mysterious behavior which isn't fully revealed by
vendor's product datasheets and whitepapers. Underlying all the important
aspects of SSD behavior are asymmetries which arise from the intrinsic
technologies and architecture inside the SSD.
Which symmetries are
most important in an SSD? - That depends on your application. But knowing
that these symmetries exist, what they are, and judging how your selected SSD
compares will give you new insights into SSD
no such thing as - the perfect SSD - existing in the market today - but
the SSD symmetry list helps you to understand where any SSD in any memory
technology stands relative to the ideal. And it explains why deviations from the
ideal can matter.
flash SSDs decision tipping point|
|Editor:- in December 2010 - I interviewed Jamon Bowen,
Director of Sales Engineering for Texas Memory Systems
and asked him about the use of SSDs in financial applications like banks and
traders - a market which he said accounts for most of their RAM SSD sales.
The company which started in RAM SSDs
over 30 years
ago - now sells more flash SSDs than RAM SSDs (even though the product
brand for both types of SSD is
RamSan.) Bowen said that flash is 70% of their business.
Bowen said that in many bank applications RAM SSDs are actually cheaper than
flash - because of the small size of the data. TMS still sell a lot of 16GB RAM
Production bank systems are typically shared by many hosts and
get a lot of write IOPS / capacity. To achieve the same
provisioning which would drive the cost up.
He suggested a simple
rule of thumb for intensive IOPS bank SSDs on the SAN
- < 128GB capacity - RAM SSDs cheaper
- 128GB to 4TB capacity - middle ground could be either - or determined by
Jamon Bowen said that the analysis
side of operations in banks is different. That tends to have much larger data
sets and is more read than write intensive. In these apps - flash SSDs are
usually more economic.
- > 4TB - flash SSDs cheaper
|HGST rekindles concept of a PCM based PCIe
Editor:- August 4, 2014 - HGST today
it will demonstrate a
PCIe SSD concept at the Flash
Memory Summit. HGST says the demonstration model delivers 3 million
random read IOPS (512 Bytes) and a random read access latency of 1.5
Micron funded the
world's first enterprise PCM PCIe SSD demo 3 years ago (in
June 2011). The
storage density of PCM resulted in an SSD which had pitifully low capacity
compared to flash memory at that time - and earlier this year (in January 2014)
that Micron had temporarily abandoned this idea.
Is HGST really
going to wander into memory space where even the memory makers don't want to go?
Or is this just a market signal that HGST isn't just looking at short term SSD
SanDisk extends the reach of its SSD software platform
July 8, 2014 - 2 weeks ago
a new enterprise software product -
ZetaScale - designed
to support large inmemory intensice applications.
I delayed writing
about it at the time - until I learned more. But now I think it could be one of
the most significant SSD software products launched in 2014 - because of the
freedom it will give big memory customers (in the next 2-3 years) about how
they navigate their tactical choices of populating their apps servers with
low latency flash SSD hardware.
what is ZetaScale?
says - "ZetaScale software's highly parallelized code supports high
throughput for flash I/O, even for small objects, and optimizes the use of CPU
cores, DRAM, and flash to maximize application throughput. Applications that
have been flash-optimized through the use of ZetaScale can achieve performance
levels close to in-memory DRAM performance."
ZetaScale is SSD
agnostic. "ZetaScale is compatible with any brand of PCIe, SAS, SATA, DIMM
or NVMe connected flash storage device, providing customers the ability to
choose, avoiding hardware vendor lock-in."
I was curious to see
how this new product - which is a toolkit for deploying flash with tiering to
DRAM as a new memory type - fitted in with other products - from SanDisk and
from other vendors which also operate in this "flash as a big
memoryalternative to DRAM" application space .
So I asked
SanDisk some questions - and got some interesting answers.
- Where does the ZetaScale product come from?
ZetaScale builds upon our
acquisition technology for additional use cases and flash deployment models.
ZetaScale allows any developer to better tune their applications for
flash-based environments, no matter which vendors hardware or interface is being
leveraged. Thus, ZetaScale represents a major step forward in our vision of the
flash-transformed data centerempowering software developers to scale and
enhance their applications to meet today's big data and real-time analytics
demands, while lowering TCO.
- How much commonality is there between ZetaScale and FlashSoft product
ZetaScale and FlashSoft software are complementary and
FlashSoft provides direct-attached flash-based
caching for NAS and SAN devices, with the goal of improving performance for
unmodified applications running on a server.
software provides a flash and multi-core optimization library that applications
can integrate to allow them to achieve 3x times the performance
improvement from flash alone.
Both ZetaScale and FlashSoft software
provide their benefits in bare metal and virtualized environments
- Does ZetaScale support ULLtraDIMM?
Yes. The software is compatible with any brand of PCIe, SAS,
SATA, DIMM or NVMe connected flash device, enabling users to avoid vendor
lock-in. However, the software does not get embedded into any SSD.
Editor's comments:- overall I'd have to rate SanDisk's -
ZetaScale as one of the most significant SSD software products launched in 2014.
- How would ZetaScale fit into a future SanDisk product line which also
SanDisk cannot comment on open M&A activity. As usual, all
planning surrounding the product portfolio and roadmap will begin following the
close of the acquisition.
From a technical point of view - it's a toolkit which will enable
architects of SSD apps servers with very large in memory databases to
decouple themselves fromdeep dives into specific low latency SSD products.
Instead of gambling on whether they should exploit particular features which
come with particular low latency SSDs - they can instead use ZetaScale as the
lowest level of flash which their apps talk to. And that will change markets.
although SanDisk didn't want to comment on how this would be positioned against
Fusion-io's VSL - it's
undeniable that in some applications it does compete today.
wouldn't be surprised to see - a year after the acquisition (if it goes ahead)
ZetaScale could be useful as a way of introducing new customers to the
ioMemory hardware environment - without those customers having to make a hard
commitment to the rest of Fusion-io's software.
And - looking at the
SSD market - it also means that SanDisk software might be a safer standard
for future customers of any DDR4 or HMC SSDs which might emerge from competitor
Micron which - unlike
SanDisk - hasn't demonstrated yet any strong ambitions in the
SSD software platform
is there a market for I'M Intelligent Memory inside SSDs?
June 4, 2014 - Are there applications in the SSD market for DRAM chips which
integrate ECC correction inside the RAM chip - and which plug into standard
That was the question put to me this afternoon by Thorsten
Wronski - whose company MEMPHIS
Electronic AG distributes I'M Intelligent Memory in
Thorsten told me he's had a good reaction from the SSD
companies he's spoken to - which is why he phoned.
But in a long
conversation about the economics and architectures of end to end
in SSDs and the different
ratios of RAM cache
to flash in SSDs - I told him that my initial reaction was he should look
at embedded applications - which depend on the
reliability of a
single SSD - rather than enterprise systems in which the economics analysis for
arrays point to a system wide solution rather than a point product fix.
interesting thing is he said he's done tests on the new I'M memory as drop in
replacements for unprotected memory designs- in which he accelerated the likely
incidence of error events by increasing the interval between refreshes and
raising the temperature.
Here's what he said.
assembled a standard 1GB unbuffered DIMM with 8 chips of 1Gbit ECC DRAM. Then we
put this into a test board and ran RSTPro (a very strong memory test software).
No error found.
Next we put the whole board into a temperature chamber
at 95°C, which normally requires the refresh rate to be doubled (32mS
instead of 64mS). No error found.
Finally we wrote a software to change the refresh-register of the CPU
on the board, so we were able to set higher values. The highest possible was
750mS, so the DRAM did almost not get any more refreshes. Still it continued
working in RSTPro without a single error for 24 hours.
We tried the same with Samsung and Hynix modules, but none of them
came even close to those results. Most failed at refresh-rates of 150 to 200 mS,
which is not bad indeed. Many more tests will follow."
Editor's comments:- the reason I mention this - is because
adapting the refresh rate was one of the things mentioned in my recent blog -
Are you ready to
However - most of the leading SSDs in
don't have RAM caches for other reasons (to reduce the physical space, power
consumption, hold-up time, or because don't need the performance). So I told
Thorsten I don't see an industry wide demand inside SSDs. But some of you
might already have thought of applications.
I'M ECC DRAM product
are you ready to adapt to new ways of thinking about enterprise
Editor:- April 2, 2014 - Are you ready to
rethink what you
think about enterprise DRAM?
The revolution in in use-case-aware intelligent flash could crossover
to DRAM. These ideas are brought together in the new home page blog on
StorageSearch.com ...read the article
A3CUBE unveils PCIe memory fabric for
10,000 node-class PCIe SSD architectures
25, 2014 -
PCIe SSDs can now
access a true PCIe connected shared memory fabric designed by A3CUBE - which exited
stealth today with the
of their remote shared broadcast memory network -
RONNIEE Express -
which provides 700nS (nanoseconds) raw latency (4 byte message) and which
enables message throughput - via standard PCIe - which is 8x better
Editor's comments:- I spoke to the
recently - who say they intend to make this an affordable mainstream
The idea of using PCIe as a fabric to share data at low
latency and with fast throughput across a set of closely located servers
isn't a new one.
The world's leading PCIe chipmaker
PLX started educating
designers and systems architects about these possibilities
few years ago - as a way to elegantly answer a new set of scalability
problems caused by the increasing adoption of PCIe SSDs. These questions
- how do you make this expensive resource available to more servers?
the least year or so - we've seen most of the leading vendors in the enterprise
PCIe SSD market leverage some of the new features in PCIe chips - to
implement high availability SSDs with low latency.
- how do you enable a simple to implement failover mechanism - so that data
remains accessible in the event of either a server or SSD fault?
But although there
are many ways of doing this - the details are different for each vendor.
- until now - if you wanted to share data at PCIe-like latency across a bunch
of PCIe SSDs from different companies - located in different boxes - the
simplest way to do that was to bridge across ethernet or infiniband. - And even
though it has been technically possible with standard software packages - the
integration, education and support issues - compared to legacy SAN or NAS
techniques would be extremely daunting.
That's where A3CUBE comes into
the picture. Their concept is to provide a box which enables any supported PCIe
device to connect to any other - at low latency and with high throughput -
in an architecture which scales to many thousands of nodes.
heart of this is a shared broadcast memory window - of 128Mbytes - which can be
viewed simultaneously by any of the attached ports.
ever used shared remote memory in a supercomputer style of system design at
any time in the past 20 years or so - you'll know that the critical thing is how
the latency grows as you add more ports. So that was one of the questions I
Here's what I was told - "The latency is related to the
dimension of the packet for example: In a real application using a range of
64-256 bytes of messages the 3D torus latency doubled after 1,000 nodes.
With larger packets, the number of nodes to double the latency becomes grater.
But the real point is that the latency of a simple p2p in a standard 10GE is
reached after 29,000 nodes.
"A more clear example of the scalability of the system is this.
Imagine that an application experiences a max latency of 4 us with 64 nodes, now
we want to scale to 1,000 nodes the max latency that the same application
experience will became 4.9 us. 0.9 us of extra latency for 936 more nodes."
Editor again:- Those are very impressive examples - and demonstrates that the
"scalability" is inherent in the original product design.
didn't want to say publicly what the costs of the nodes and the box are at this
stage. But they answered the question a different way.
Their aim is to
price the architecture so that it works out cheaper to run than the legacy
(pre-PCIe SSD era) alternatives - and they're hoping that server oems and fast
SSD oems will find A3CUBE's way of doing this PCIe fabric scalability stuff -
is the ideal way they want to go.
There's a lot more we have to learn
- and a lot of testing to be done and software to be written - but for users
whose nightmare questions have been - how do I easily scale up to a 10,000
PCIe SSD resource - and when I've got it - how can I simplify changing
suppliers? - there's a new safety net being woven. Here are the
3.5" RAM SSDs - from OCZ?
Editor:- December 13,
2013 - It's been
since I last heard any SSD makers talking about launching new
RAM SSDs - but the idea
has resurfaced in a blog -
Clouds the Times They are a Changing - by Ravi Prakash,
Director of Product Management - OCZ - who says such
devices might be useful in write intensive applications such as a ZFS intent
Ravi said he's interested in hearing from anyone who might
be interested in a future RAM SSD concept - he calls Aeon - which "will
deliver 140,000 sustained
4KB blocks and media latency of less than 5 µsec in a familiar 3.5
drive form factor." ...read the
See also:- on the subject of the name Aeon -
and more like this - take a look at
Speed and Strength Metaphors in SSD brands
McObject shows in-memory database resilience in NVDIMM
October 9, 2013 - what happens if you pull out the power plug during
intensive in-memory database transactions? For those who don't want to rely on
batteries - but who also need ultimate speed - this is more than just an
Recently on these pages I've been talking a lot
about a new type of
SSDs which are hoping to break into the application space owned by
PCIe SSDs. But another
solution in this area has always been DRAM with power fail features which save
data to flash in the event of
loss. (The only disadvantages being that the memory density and cost are
constrained by the nature of DRAM.)
products include in-memory database software) yesterday
published the results of
benchmarks using AGIGA
Tech's NVDIMM in which
they did some unthinkable things which you would never wish to try out for
yourself - like rebooting the server while it was running... The result?
Everything was OK.
"The idea that there must be a tradeoff
between performance and persistence/durability has become so ingrained in the
database field that it is rarely questioned. This test shows that mission
critical applications needn't accept latency as the price for recoverability.
Developers working in a variety of application categories will view this as a
breakthrough" said Steve Graves,
Here's a quote from the whitepaper -
Persistence, Without The Performance Penalty (pdf) - "In these tests
eXtremeDB's inserts and updates with AGIGA's NVDIMM for main memory storage
were 2x as fast as using the same IMDS with transaction logging, and
approximately 5x faster for database updates (and this with the
transaction log stored on RAM-disk, a solution that is (even) faster than
storing the log on an SSD). The possibility of gaining so much speed while
giving up nothing in terms of data durability or recoverability makes the IMDS
with NVDIMM combination impossible to ignore in many application categories,
including capital markets, telecom/networking, aerospace and industrial
Editor's comments:- last year McObject
published a paper showing the benefits of using PCIe SSDs for the transaction
log too. They seem to have all angles covered for mission critical ultrafast
databases that can be squeezed into memory.
in memory database even better with FIO's flash
November 20, 2012 - McObject
recently released new
benchmark results which indicate that the in-memory database company is not
so unfriendly to flash SSDs as you may have thought from reading earlier
company positioning papers.
It seems that a software product - which
was originally designed for the DRAM-HDD world - is a good fit in the flash SSD
world too - if you have the right scale of data and the right SSD. ...read more
Micron sources power holdup technology for NVDIMMs
November 14, 2012 - Micron
has signed an agreement
with AgigA Tech
to collaborate to develop and offer nonvolatile DIMM (NVDIMM) products using
AgigA's PowerGEM (sudden power loss
controller and holdup modules).
STEC discloses RAM vs flash SSD revenues
November 7, 2012 - among other things STEC revealed
yesterday in its earnings conference call that RAM SSDs were approximately 4%
of its revenues in the recent quarter.
AMD will rebrand Dataram's RAMDisk software
September 6, 2012 - Dataram
it will develop a version of its RAMDisk software which will be rebranded
by AMD in Q4 under the name of Radeon
RAMDisk and will target Windows market gaming enthusiasts seeking (upto 5x)
faster performance when used with enough memory. See also:-
Kaminario recommends you read SSD Symmetries article
June 15, 2012 - I accidentally discovered today that earlier this week Gareth Taube,
VP of Marketing at Kaminario
published a new blog
in which he recommends my article about
says "Flexibility, such as being able to integrate multiple memory
technologies into a single box (like Kaminario's K2-H), is going to be
increasingly important to customers who want efficiency and customization
options. This is especially true because there are many memory innovations
coming on the near horizon." ...read Gareth's blog
comments:- when I was writing the symmetry article one of the things I had in
mind to do was to put more examples in it. Then I realized that having lots of
examples would simply make the article unreadable.
One of the examples
I was going to use for good roadmap symmetry (but then forgot to put
anywhere) was in fact Kaminario - because they can leverage off whatever
Fusion-io does with
flash (or other nv memory)
and furthermore Kaminario can also leverage off whatever server makers do with
CPUs and RAM. Roadmap
symmetry is a long term consideration - important for big users who don't like
supplier churn and important for
VCs and investors too.
I'm glad I wrote that bit about "roadmap symmetry" - because by a
spooky coincidence - 3 days later we got the news that Kaminario's investors
still love what they do.
June 18, 2012 - Kaminario today
it has secured a $25 million series D round of funding, bringing its total
funding to $65 million.
sharpen your SSD R/W grid latency weapons to 5µS
May 9, 2012 - Kove
has published some
record latency numbers for its fast
RAM SSD - the XPD L2 -
which has achieved continuous and sustained 5 microsecond random storage read
and write when connected via 40Gb/s
from Mellanox .
Kove's system has good
which the company says - is not subject to periodic performance jitter or "periodicity".
Even under constantly changing disk utilization, it delivers uniform,
predictable, and deterministic performance.
"The Kove XPD L2... allows high performance applications to use
storage as a weapon rather than accept it as a handicap," said Kove's
Overton. "We are pleased to set a new bar height for storage
sudden power loss|
|Why should you care
what happens in an SSD when the power goes down? |
This important design
feature - which barely rates a mention in most SSD datasheets and press releases
- has a strong impact on
SSD data integrity
This article will help you understand why some
SSDs which (work perfectly well in one type of application) might fail in
others... even when the changes in the operational environment appear to be
|sometimes you just can't wait|
| "Across the whole
enterprise - a single petabyte of SSD with new software could replace 10 to
50 petabytes of raw legacy HDD storage and still enable all the apps to run
|the enterprise SSD
software event horizon|
|the Problem with
Write IOPS in flash SSDs |
|Random "write IOPS"
in many of the fastest
flash SSDs are now similar to "read IOPS" - implying a
performance symmetry which was once believed to be impossible.|
are flash SSD IOPS such a poor predictor of application performance? And why
are users still buying
RAM SSDs which cost an
order of magnitude more than SLC? (let alone
MLC) - even
when the IOPS specs look superficially similar?
tells you why the specs got faster - but the applications didn't.
||And why competing SSDs with
apparently identical benchmark results can perform completely differently.