2. Acunu: Understanding Massive Data.
We are witnessing at least two revolutions in storage: (1) massive datasets and workloads, and (2) the rise of
scale-out commodity hardware. This whitepaper describes the Acunu Data Platform, and how Acunu is allowing
massive data workloads to take full advantage of
today’s hardware.
Acunu is rewriting the storage stack in the Linux ker-
nel for Massive Data thanks to world-class engineer-
ing and algorithms research.
Massive Data Workloads.
How have workloads changed? The workloads de-
manded by hardware of massive datasets typically
exhibit three main features:
• Continuously high ingest rates (many thousands of
updates/s, typically high-entropy, random updates)
• Individual pieces of data are small, and aren’t valu-
able in isolation (for example, stock ticks or ses-
sion IDs)
• Continual range queries are important for analyt-
ics (such as demanded by Apache Hadoop)
This is in stark contrast to the ‘load, then query’
regimes of more traditional databases.
Understanding massive data means being able to
extract features and trends, all the time while the
data is continually updated. Existing platforms and
solutions cannot do this at scale, with predictably
high performance. This is where Acunu comes in.
The first revolution is the rise of non-relational, or
‘nosql’ data bases such as Cassandra, and analyt-
ics frameworks and tools such as Hadoop. The driving force is using clusters of commodity machines to ingest large
volumes of data, process it, and serve it. Previous technologies such as mysql are traditionally cumbersome to operate
at the scales needed here. For many deployments in both enterprise and non-enterprise settings, these technologies
are likely to account for the majority of data stored where features such as high availability at low cost are more impor-
tant than transactional durability.
The second revolution is a hardware one. Commodity machines now typically possess many cores, and bear closer
resemblence to a supercomputer of the 90s than a desktop of the same era. Hard drive capacity and sequential band-
width has been doubling every 18 months, as predicted; yet random IO performance has not improved. Solid-state
drives (SSDs) offer 2-3 orders of magnitude better random IO performance than hard drives. Clearly these have huge
potential to revolutionize the database world, if only the software stack can harness and utilize their performance.

3. Acunu’s proposition - reengineering the stack for massive data.
These two revolutions expose a new
problem. The “storage stack” that
abstracts away details of the hard-
ware and allows applications to
communicate with the hardware, is
now a serious bottleneck. It was built
for the needs of databases and hard-
ware of the 90s. The result is that it
presents fundamentally the wrong
abstraction for Massive Data applica-
tions, which developers either work
around or accept, and secondly, it
simply cannot be easily modified to
take advantage of new storage tech-
nologies - the assumptions underlying
rotational drives are implicit through-
out it.
Acunu is taking the difficult, but fun-
damental, step of reengineering the
storage stack for the age of Massive
Data. We’ve thrown almost 30 world-class engineers, including over 10 PhDs, mathematicians, Cambridge, Oxford and
Stanford academics at the problem. The result is a set of core components, rearchitected from the ground up.
Why is this important?
“It’s disruptive if it’s a 10x benefit, because that’s a platform for creating opportunities for new ecosystems.”
- Reid Hoffman, Data as Web 3.0 (SXSW 2011)
By revisiting the core storage stack,
Acunu is able to provide a platform for
Massive Data applications. This al-
lows us to do things such as improve
Apache Cassandra performance by
almost 100x for heavy workloads, give
it predictable performance (removing
memory garbage collection prob-
lems), support SSDs with high write
writes and guaranteed endurance,
interoperate simultaneous Massive
Data stores (do you want to ingest via
memcached and analyze via Cassan-
dra?), offer fundamentally new fea-
tures (such as full versioning - snap-
shots and clones - while doing fast
inserts) via patented algorithms, and
lots more.
We don’t need yet another database - we need a firm foundation on which to understand massive data.

4. Acunu Data Platform.
The Acunu Data Platform is a powerful storage solution that brings simpler, faster and more predictable performance to
NOSQL stores like Apache Cassandra.
Our view is that the new data intensive
workloads that are increasingly com-
mon are a poor match for the legacy
storage systems they tend to run on.
These systems are built on a set of
assumptions about the capacity and
performance of hardware that are sim-
ply no longer true. The Acunu Data
Platform is the result of a radical re-
think of those assumptions; the result is
high performance from low cost com-
modity hardware.
Open Storage Core.
The Acunu Storage Core is an open-
source, in-kernel, industrial-strength,
write-optimized, multi-dimensional,
fully-versioned, key-value store. It con-
tains the majority of our techniques that provide extremely high, predictable performance. It is open-source under
GPLv2, and can be downloaded for free from www.acunu.com.
Interoperability of multiple data stores.
By running on the Acunu Data Platform, we are able to allow multiple data stores to interoperate. For example, applica-
tions can write to the store using memcached (running on Acunu), and then perform analysis on the same data using
Apache Cassandra, or the Hadoop framework (running on Acunu). Using Acunu’s versioning and advanced isolation
tools, views of large data sets can be updated atomically and isolated from one another.
Powered by Acunu.
We provide user-level client libraries to allow applications to run on the Storage Core. Typically, a small patch or plugin
is required in order for the application to use the Acunu client libraries. Version 1 ships with the Acunu Distribution for
Apache Cassandra, and a large object store that talks the same protocol as Amazon’s S3 store, based on Project
Voldemort. As time goes on, we will release more patches, and we will look to the community to contribute patches for
various projects. We will make all these open, and freely-available.

5. Monitor and control the entire stack, over
the whole cluster.
To make all of this easier to use, we have also
produced some snazzy management tools.
These are web-based and follow the same de-
centralized model of Cassandra: simply point
your web browser at any of the boxes running
Acunu’s software and you will be able to create
a cluster, do snapshots and clones, or see what
is happening across your Acunu storage nodes.
Since the Acunu platform replaces the file sys-
tem and page cache, it has direct hardware
access and unprecedented hardware visibility.
This means that Acunu’s monitoring tools can
observe and directly control such things as disk
queues, latencies throughout the stack, and much more. One can quickly diagnose hardware bottlenecks, and ineffi-
ciencies up and down the stack, across the entire cluster.

6. Fundamental research = new possibilities.
The Acunu Storage Core is based on fundamental, patent-pending, algorithms and engineering research. This isn’t just
a better implementation of an existing idea, or about a shinier UI or management console (although our management
stack is also pretty cool). We are doing world-class research, engineering, patenting, and we publish at top confer-
ences. Why? This allows us to do things simply not
possible before. Here are some examples.
Fast, full versioning.
Versioning of large data sets is an incredibly powerful
tool. Not just low-performance snapshots for back-
ups, but high-performance, concurrent-accessible
clones and snapshots of live datasets for test and
development, offering many users different, writeable,
views of the same large dataset, going back in time,
and much more.
Traditionally, the state-of-the-art in algorithms for ver-
sioning large data sets is based on a data structure
known as the ‘copy-on-write B-tree’ (CoW B-tree) -
this is ubiquitous in file systems and databases in-
cluding ZFS, WAFL, Btrfs, and more. The CoW B-tree (and most of its variants, such as append-only trees, log file sys-
tems, redirect-on-write, etc.) has three fundamental problems - (1) it is space-inefficient (and thus requires frequent
garbage collection); (2) it relies on random IO to scale (and thus performs poorly on rotational drives); and (3) it cannot
perform fast updates, even on SSDs.
Acunu has invented a fundamentally new data structure - the Stratified B-tree - that addresses all the above problems.
Some details of this revolutionary data structure have been published: see [Twigg, Byde - Stratified B-trees and ver-
sioned dictionaries, USENIX HotStorage’11].
Designed for SSDs
Existing storage schemes do not address the fact that SSDs require addressing in a fundamentally different way. Al-
though they present a SATA/SAS interface and are sector-addressed, this is only to allow them to be a drop-in replace-
ment for hard drives. Extracting maximum performance and lifetimes requires two things: (1) the storage stack to un-
derstand how they operate; and (2) new data structures and algorithms that exploit their design characteristics.
By understanding how SSDs fundamentally work, Acunu has been able to engineer data structures that allow unprece-
dented long-term write performance, while guaranteeing device endurance.
Not just peak performance, but predictable performance.
By eliminating JVM-based garbage collection and memory management issues, and carefully controlling hardware ac-
cess from within the Linux kernel, Acunu is able to offer predictably high performance, even under sustained high loads,
with both ingest and analytic range queries - the perfect ingredients for any real-time analytics platform. Watch carefully
in future versions as Acunu begins to deploy fundamentally new offerings here, exploiting our back-end algorithmic
advantage.

7. V1: Supercharging Apache Cassandra with Acunu.
A major feature of the Acunu Storage Core is its predictably high performance, even under sustained heavy load. Often,
this is more important than absolute peak performance figures - if you know what to expect from a node, then you can
add nodes to get the desired performance level. On the other hand, if performance is unpredictable, how many nodes
should you use?
The graphs below show the difference between Acunu’s Distribution for Cassandra and Vanilla Apache Cassandra, un-
der a sustained heavy load of 50k inserts/second. It is easy to see the advantage of Acunu - the worst-case latency is
never worse than 18ms, whereas for Apache Cassandra it often exceeds 10,000ms.
Next, we consider the performance of range
queries under sustained insert load. Immedi-
ately after performing the inserts above, we
attempted to perform a large sequence of small
range queries, simulating a real-time analytics
workload.
The graph on the right shows the result. With
Acunu, Cassandra was able to sustain over 40
range queries per second (this is an area we
have not optimized for V1, and will dramatically
improve in a later release). Apache Cassandra,
by contrast, manages about 0.3 queries per
second. After about 1 hours, this improves
slightly since we manually triggered a ‘major
compaction’ (in practise, this is not possible
during sustained inserts).

8. Licensing, Pricing, Support.
At launch, the Acunu Data Platform will come in two flavors:
Enterprise Edition: The full Acunu stack, with either regular (5x8) or premium (24x7) support via phone, email
and web at support.acunu.com. Please contact sales@acunu.com for details.
Standard Edition: Same as Enterprise Edition, but limited to 2 nodes, with mailing list / community support.
Free for production use.
Tested and supported.
Whatever edition and level of support you opt for, we are committed to making sure the product you use is rock-solid,
and ready for prime-time production use. Unlike other vendors of open-source software, the free version and enterprise
version of the Acunu Storage Core are the same thing, both builds subjected to the same rigorous testing and QA, in-
volving over 300 machine-hours of tests per build. Even if you use the Standard Edition, we provide detailed support
through user and developer mailing lists. For the Enterprise Edition, we offer unparalleled access to our team of support
engineers, and world-class engineers and PhDs via support.acunu.com.
Open-source.
We recognize the importance of the open source community in developing, maintaining, innovating and educating
around complex and fundamental software projects. We also recognize that, in order to become strongly adopted, our
most fundamental code should be open for anyone to examine and improve. That’s why we’re making the Acunu Stor-
age Core open-source, under the GPLv2. All our our contributions to Apache Cassandra and other open-source pro-
jects will be released under the appropriate licenses, too. The rest of the Acunu Data Platform, including the enterprise-
grade management and monitoring tools, and additional performance packs, will be released in due course.
Community.
Acunu is committed to contributing back to the open-source communities for the products we use, and to leverage
their ability to strengthen and develop our own open-source projects (such as the Acunu Storage Core and others com-
ing in the future). We welcome all contributions and developments from the community.

9. About Acunu.
Acunu is reengineering the storage stack from the ground-up for the age of Massive Data. Based on fundamental algo-
rithms research and world-class engineering, the Acunu Platform allows applications such as Apache Cassandra and
Hadoop, along with many others, to (1) drive today’s commodity hardware harder than ever before, including many-core
architectures, SSDs and large SATA drives; (2) exploit new features in the Acunu Core (such as fast cloning and version-
ing); and (3) obtain predictable, reliable high performance. Storage is the key to understanding Massive Data, and gain-
ing competitive advantage. The Acunu Open Platform lets companies do this quicker, easier and cheaper.
Acunu was founded in 2009 by researchers and engineers from Cambridge, Oxford, and several well-known high-tech
companies. We are backed by some of Europe’s top VCs, with total funding over $5.0M. We are based in London and
California.
Founders.
Dr Tim Moreton, CEO: Tim is an expert in distributed file systems. He holds a PhD from Cambridge, where he built a
distributed file system for the Xen project. He was previously at Tideway (now BMC), where he was lead engineer on a
number of data center projects.
Dr Andy Twigg, CTO: Andy has an outstanding track record of theoretical and applied computing research. He has
held positions at Cambridge University, Microsoft Research, Thomson Research and Oxford University. His PhD in 2006
on compact routing algorithms was nominated for the BCS Best Dissertation Award. He holds a Junior Research Fel-
lowship at Oxford University, where he is a member of the CS department.
Tom Wilkie, VP Engineering: Tom was one of the first UK employees at XenSource before its acquisition by Citrix in
2007. He worked on the XenCenter management stack and numerous customer projects. He has a BA in Computer
Science from Cambridge.
Dr John Wilkes, Technical Advisor: John is an advisor to Acunu. John led the Storage Systems group at HP Labs for
15 years, before moving to Google in 2008. John received his PhD from Cambridge in 1984, an Outstanding Contribu-
tion award from SNIA in 2001 and was made an ACM Fellow in 2002.