Has EMC stooped so low that they have to resort to Hitachi math for their latest performance claims?
Readers might remember that just a few months ago, I had a blog post [Is this what HDS tells our mainframe clients?] pointing out the outlandish comparison Hitachi was using in their presentations. Their response was to cover it up, forcing me to follow up with my post [The Cover-up is worse than the original crime]. To their credit, they eventually removed the false and misleading information from their materials.
Now an avid reader of my blog has brought this to my attention. Apparently,
EMC has been showing customers a presentation
[Accelerating Storage Transformation with VMAX and VPLEX] with false and misleading comparison claims between IBM DS8000, HDS VSP and EMC VMAX 40K disk system performance.
(FTC Disclosure: This would be a good time to remind my readers that I work for IBM and own IBM stock. I do not endorse any of the EMC or HDS products mentioned in this post, and have no financial affiliation or investments directly with either EMC nor HDS. I am basing my information solely on the presentation posted on the internet and other sources publicly available, and not on any misrepresentations from EMC speakers at the various conferences where these charts might have been shown.)
The problem with misinformation is that it is not always obvious. The EMC presentation is quite pretty and professional-looking. It is the typical slick, attention-getting, low-content, over-simplified marketing puffery you have come to expect from EMC. There are two slides in particular that I have issue with.
This first graphic implies that IBM and HDS are nearly tied in performance, but that EMC VMAX 40K has nearly triple that bandwidth. Overall the slide has very little detail. That makes it difficult to determine what exactly is being claimed and whether a fair comparison is being made.
- The title claims that VMAX 40K is "#1 in High Bandwidth Apps". Only three disk systems are shown so the claim appears to be relative to only the three systems. The wording "High Bandwidth Apps" is confusing considering the cited numbers are for disk systems and no application is identified. By comparison, IBM SONAS can drive up to 105 GB/sec sequential bandwidth, nearly double what EMC claims for its VMAX 40K, so EMC is certainly not even close to #1.
- Is the workload random or sequential? That is not easy to determine. The use of "GB/s" along with the large block size of 128KB implies the I/O workload is sequential, which is great for some workloads like high performance computing, technical computing and video broadcasts. Random workloads, on the other hand, are usually measured in I/Os per second (IOPS) with a block size ranging 4KB to 64KB. (I am assuming the 128K blocks refers to 128KB block size, and not reading the same block of cache 128,000 times.)
- The slide states "Maximum Sustainable RRH Bandwidth 128K Blocks". The acronym "RRH" is not defined; but I suspect this refers to "random read hits". For random workloads, 100 percent random read hits from cache represents one corner of the infamous "four corners" test. Real-world workloads have a mix of reads and writes, and a mix of cache hits and cache misses. It is also unclear whether the hits are from standard data cache or from internal buffers in adapters (perhaps accessing the same blocks repeatedly) or something else. So is this really for a random workload, or a sequential workload?
(The term "Hitachi Math" was coined by an EMC blogger precisely to slam Hitachi Data Systems for their blatant use of four-corners results, claiming that spouting ridiculously large, but equally unrealistic, 100 percent random read hit results don't provide any useful information. I agree. There are much better industry-standard benchmarks available, such as SPC-1 for random workloads, SPC-2 for sequential workloads, and even benchmarks for specific applications, that represent real-world IT environments. To shame HDS for their use of four-corners results, only for EMC themselves to use similar figures in their own presentation is truly hypocritical of them!)
- The IBM system is identified as "DS8000". DS8000 is a generic family name that applies to multiple generations of systems first introduced in 2004. The specific model is not identified, but that is critical information. Is this a first generation DS8100, or the latest DS8800, or something in between?
The slide says "Full System Configs", but that is not defined and configuration details are not identified. Configuration details, also critical information in assessing system performance capabilities, are not specified. If the EMC box costs seven times more than IBM or HDS, would you really buy it to get 3x more performance? Is the EMC packed with the maximum amount of SSD? Were there any SSD in the IBM or HDS boxes to match?
The source of the claimed IBM DS8000 performance numbers is not identified. Did they run their own tests? While I cannot tell, the VMAX may have been configured with 64 Fibre Channel 8Gbps host connections. In that case each channel is theoretically capable of supporting about 800 MB/s at 100% channel utilization. Multiplying 64 x 800MB/s = 51.2GB/s, so did EMC just do the performance comparison on the back of a napkin, assuming there are no other bottlenecks in the system? Even then, I would not round up 51.2 to 52!
- Response times were not identified. For random I/Os, response time is a very important metric. It is possible that the Symmetrix was operating with some resources at 100% utilization to get the highest GB/s result, but that would likely make I/O response times unacceptable for real-world random I/O workloads.
IBM and HDS have both published Storage Performance Council [SPC] industry-standard performance benchmarks. EMC has not published any SPC benchmarks for VMAX systems. If EMC is interested in providing customers with audited, detailed performance information along with detailed configuration information, all based on benchmarks designed to represent real-world workloads, EMC can always publish SPC benchmark results as IBM and other vendors have done. In past blog fights, EMC resorts to the excuse that SPC isn't perfect, but can they really argue that vague and unrealistic claims cited in its presentation are better?
The second graphic is so absurd, you would think it came directly from Larry Ellison at an Oracle OpenWorld keynote session. EMC is comparing a configuration with VMAX 40K plus an EMC VFCache host-side flash memory cache card to a configuration with an IBM and HDS disk system without host-side flash memory cache also configured. The comparison is clearly apples-to-oranges. Other disk system configuration details are also omitted.
FAST VP is EMC's name for its sub-volume drive tiering feature, comparable to IBM Easy Tier and Hitachi's Dynamic Tiering. The graph implies that IBM and HDS can only achieve a modest increment improvement from their sub-volume tiering. I beg to differ. I have seen various cases where a small amount of SSD on IBM DS8000 series can drastically improve performance 200 to 400 percent.
The "DBClassify" shown on the graph is a tool run as part of an EMC professional services offering called Database Performance Tiering Assessment, makes recommendations for storing various database objects on different drive tiers based on object usage and importance. Do you really need to pay for professional services? With IBM Easy Tier, you just turn it on, and it works. No analysis required, no tools, no professional services, and no additional charge!
- VFCache is an optional product from EMC that currently has no integration whatsoever with VMAX. A fair comparison would have included a host-side flash memory cache (from any vendor) when the IBM or HDS storage system was configured. Or leave it out altogether and just focus on the sub-volume tiering comparison.
Keep in mind that EMC's VFCache supports only selected x86-based hosts. IBM has published a [Statement of Direction] indicating that it will also offer this for Power systems running AIX and Linux host-side flash memory cache integrated with DS8000 Easy Tier.
I feel EMC's claims about IBM DS8000 performance are vague and misleading. EMC appears to lack the kind of technical marketing integrity that IBM strives to attain.
Since EMC is not able or willing to publish fair and meaningful performance comparisons, it is up to me to set the record straight and point out EMC's failings in this matter.
Reminder: It's not to late to register for my Webcast "Solving the Storage Capacity Crisis" on Tuesday, September 25. See my blog post [Upcoming events in September] to register!
technorati tags: IBM, DS8000, DS8800, HDS, VSP, EMC, VMAX, Symmetrix, VFCache, Easy Tier, FAST VP
Wrapping up my coverage of the annual [2010 System Storage Technical University], I attended what might be perhaps the best session of the conference. Jim Nolting, IBM Semiconductor Manufacturing Engineer, presented the new IBM zEnterprise mainframe, "A New Dimension in Computing", under the Federal track.
The zEnterprises debunks the "one processor fits all" myth. For some I/O-intensive workloads, the mainframe continues to be the most cost-effective platform. However, there are other workloads where a memory-rich Intel or AMD x86 instance might be the best fit, and yet other workloads where the high number of parallel threads of reduced instruction set computing [RISC] such as IBM's POWER7 processor is more cost-effective. The IBM zEnterprise combines all three processor types into a single system, so that you can now run each workload on the processor that is optimized for that workload.
- IBM zEnterprise z196 Central Processing Complex (CPC)
Let's start with the new mainframe z196 central processing complex (CPC). Many thought this would be called the z11, but that didn't happen. Basically, the z196 machine has a maximum 96 cores versus z10's 64 core maximum, and each core runs 5.2GHz instead of z10's cores running at 4.7GHz. It is available in air-cooled and water-cooled models. The primary operating system that runs on this is called "z/OS", which when used with its integrated UNIX System Services subsystem, is fully UNIX-certified. The z196 server can also run z/VM, z/VSE, z/TPF and Linux on z, which is just Linux recompiled for the z/Architecture chip set. In my June 2008 post [Yes, Jon, there is a mainframe that can help replace 1500 servers], I mentioned the z10 mainframe had a top speed of nearly 30,000 MIPS (Million Instructions per Second). The new z196 machine can do 50,000 MIPS, a 60 percent increase!
(Update: Back in 2007, IBM and Sun mutually supported [OpenSolaris on an IBM System z mainframe]. Unfortunately, after Oracle acquired Sun, the OpenSolaris Governing Board has [grown uneasy over Oracle's silence] about the future of OpenSolaris on any platform. The OpenSolaris [download site] identifies 2009.06 as the latest release, but only for x86 and SPARC chip sets. Apparently, the 2010.03 release expected five months ago in March has slipped. Now it looks official that [OpenSolaris is Dead].)
The z196 runs a hypervisor called PR/SM that allows the box to be divided into dozens of logical partitions (LPAR), and the z/VM operating system can also act as a hypervisor running hundreds or thousands of guest OS images. Each core can be assigned a specialty engine "personality": GP for general processor, IFL for z/VM and Linux, zAAP for Java and XML processing, and zIIP for database, communications and remote disk mirroring. Like the z9 and z10, the z196 can attach to external disk and tape storage via ESCON, FICON or FCP protocols, and through NFS via 1GbE and 10GbE Ethernet.
- IBM zEnterprise BladeCenter Extension (zBX)
There is a new frame called the zBX that basically holds two IBM BladeCenter chassis, each capable of 14 blades, so total of 28 blades per zBX frame. For now, only select blade servers are supported inside, but IBM plans to expand this to include more as testing continues. The POWER-based blades can run native AIX, IBM's other UNIX operating system, and the x86-based blades can run Linux-x86 workloads, for example. Each of these blade servers can run a single OS natively, or run a hypervisor to have multiple guest OS images. IBM plans to look into running other POWER and x86-based operating systems in the future.
If you are already familiar with IBM's BladeCenter, then you can skip this paragraph. Basically, you have a chassis that holds 14 blades connected to a "mid-plane". On the back of the chassis, you have hot-swappable modules that snap into the other side of the mid-plane. There are modules for FCP, FCoE and Ethernet connectivity, which allows blades to talk to each other, as well as external storage. BladeCenter Management modules serve as both the service processor as well as the keyboard, video and mouse Local Console Manager (LCM). All of the IBM storage options available to IBM BladeCenter apply to zBX as well.
Besides general purpose blades, IBM will offer "accelerator" blades that will offload work from the z196. For example, let's say an OLAP-style query is issued via SQL to DB2 on z/OS. In the process of parsing the complicated query, it creates a Materialized Query Table (MQT) to temporarily hold some data. This MQT contains just the columnar data required, which can then be transferred to a set of blade servers known as the Smart Analytics Optimizer (SAO), then processes the request and sends the results back. The Smart Analytics Optimizer comes in various sizes, from small (7 blades) to extra large (56 blades, 28 in each of two zBX frames). A 14-blade configuration can hold about 1TB of compressed DB2 data in memory for processing.
- IBM zEnterprise Unified Resource Manager
You can have up to eight z196 machines and up to four zBX frames connected together into a monstrously large system. There are two internal networks. The Inter-ensemble data network (IEDN) is a 10GbE that connects all the OS images together, and can be further subdivided into separate virtual LANs (VLAN). The Inter-node management network (INMN) is a 1000 Mbps Base-T Ethernet that connects all the host servers together to be managed under a single pane of glass known as the Unified Resource Manager. It is based on IBM Systems Director.
By integrating service management, the Unified Resource Manager can handle Operations, Energy Management, Hypervisor Management, Virtual Server Lifecycle Management, Platform Performance Management, and Network Management, all from one place.
- IBM Rational Developer for System z Unit Test (RDz)
But what about developers and testers, such as those Independent Software Vendors (ISV) that produce mainframe software. How can IBM make their lives easier?
Phil Smith on z/Journal provides a history of [IBM Mainframe Emulation]. Back in 2007, three emulation options were in use in various shops:
- Open Mainframe, from Platform Solutions, Inc. (PSI)
- FLEX-ES, from Fundamental Software, Inc.
- Hercules, which is an open source package
None of these are viable options today. Nobody wanted to pay IBM for its Intellectual Property on the z/Architecture or license the use of the z/OS operating system. To fill the void, IBM put out an officially-supported emulation environment called IBM System z Professional Development Tool (zPDT) available to IBM employees, IBM Business Partners and ISVs that register through IBM Partnerworld. To help out developers and testers who work at clients that run mainframes, IBM now offers IBM Rational Developer for System z Unit Test, which is a modified version of zPDT that can run on a x86-based laptop or shared IBM System x server. Based on the open source [Eclipse IDE], the RDz emulates GP, IFL, zAAP and zIIP engines on a Linux-x86 base. A four-core x86 server can emulate a 3-engine mainframe.
With RDz, a developer can write code, compile and unit test all without consuming any mainframe MIPS. The interface is similar to Rational Application Developer (RAD), and so similar skills, tools and interfaces used to write Java, C/C++ and Fortran code can also be used for JCL, CICS, IMS, COBOL and PL/I on the mainframe. An IBM study ["Benchmarking IDE Efficiency"] found that developers using RDz were 30 percent more productive than using native z/OS ISPF. (I mention the use of RAD in my post [Three Things to do on the IBM Cloud]).
What does this all mean for the IT industry? First, the zEnterprise is perfectly positioned for [three-tier architecture] applications. A typical example could be a client-facing web-server on x86, talking to business logic running on POWER7, which in turn talks to database on z/OS in the z196 mainframe. Second, the zEnterprise is well-positioned for government agencies looking to modernize their operations and significantly reduce costs, corporations looking to consolidate data centers, and service providers looking to deploy public cloud offerings. Third, IBM storage is a great fit for the zEnterprise, with the IBM DS8000 series, XIV, SONAS and Information Archive accessible from both z196 and zBX servers.
To learn more, see the [12-page brochure] or review the collection of [IBM Redbooks]. Check out the [IBM Conferences schedule] for an event near you. Next year, the IBM Storage University will be held July 18-22, 2011 in Orlando, Flordia.
technorati tags: IBM, Technical University, zEnterprise, x86, POWER7, RISC, z/OS, Linux, AIX, OpenSolaris, Oracle, FICON, NFS, z196, zBX, DB2, SAO, IEDN, INMN, RDz, ISV, Eclipse, Cloud Computing
The IBM Challenge was a big success. One of the contestants, Ken Jennings, [welcomes our new computer overlords]. Congratulations are in order to the IBM Research team who pulled off this Herculean effort!
Some folks have poked fun at some of the odd responses and wager amounts from the IBM Watson computer during the three-day tournament. Others were surprised as I was that the impressive feat was done with less than 1TB of stored data. Here is what John Webster wrote in CNET yesterday, in hist article [What IBM's Watson says to storage systems developers]:
"All well and good. But here's what I find most interesting as a result of what IBM has done in response to the Grand Challenge that motivated Watson's creators. We know, from Tony Pearson's blog, that the foundation of Watson's data storage system is a modified IBM SONAS cluster with a total of 21.6TB of raw capacity. But Pearson also reveals another very significant, and to me, surprising data point: "When Watson is booted up, the 15TB of total RAM are loaded up, and thereafter the DeepQA processing is all done from memory. According to IBM Research, the actual size of the data (analyzed and indexed text, knowledge bases, etc.) used for candidate answer generation and evidence evaluation is under 1 Terabyte."
What Pearson just said is that the data set Watson actually uses to reach his push-the-button decision would fit on a 1TB drive. So much for big data?"
To better appreciate how difficult the challenge was, and how a small amount of data can answer a billion different questions, I thought I would cover Business Intelligence, Data Retrieval and Text Mining concepts.
Let's start with Business Intelligence.
[Seth Grimes] pointed me to this quote from [A Business Intelligence System], written by Hans Peter Luhn back in October 1958 IBM Journal.
"In this paper, business is a collection of activities carried
on for whatever purpose, be it science, technology,
commerce, industry, law, government, defense, et cetera.
The communication facility serving the conduct of a business
(in the broad sense) may be referred to as an intelligence
system. The notion of intelligence is also defined
here, in a more general sense, as the ability to apprehend
the interrelationships of presented facts in such a way as
to guide action towards a desired goal."
Ideally, when you need "Business Intelligence" to help you make a better decision, you perform data retrieval from a structured database for the specific information you are looking for. In other cases, you might be looking for insight, patterns or trends. In that case, you go "data mining" against your structured databases.
Here's a simple example. John runs a fruit stand. One day, he kept track of how many apples and oranges were bought by men and women. How many questions can we ask against this small set of data? Let's count them:
- How many apples were sold to men?
- How many apples were sold to women?
- How many oranges were sold to men?
- How many oranges were sold to women?
But wait! For each row and column, we can combine them into totals.
- How many apples were sold in total?
- How many oranges were sold in total?
- How many fruit in total were sold to men?
- How many fruit in total were sold to women?
- How many fruit in total were sold?
|Total||63||50%||63||50%||126||But wait, there's more! Each row and column can be evaluated for relative percentages, as well as percentages of each cell compared to the total. You could make five relevant pie-charts from this data. This results in 16 more questions, such as:
- Of the fruit purchased by men, what percentage for apples?
- Of all the apples purchased, what percentage by women?
And that's not including more ethereal questions, such as:
- Are there gender-specific preferences for different types of fruit?
- What type of fruit do men prefer?
This is just for a small set, two market segments (by gender) and two products (apples and oranges). However, if you have many market segments (perhaps by age group, zip code, etc.) and many products, the number of queries that can be supported is huge. For small sets of data, you can easily do this with a spreadsheet program like IBM Lotus Symphony or Microsoft Excel.
(Photo courtesy of [OLAP, Cubes and Multidimensional Analysis] by Andrew Fryer.)
But why limit yourself to two dimensions? The above example was just for one day's worth of activity, if John captures this data for every day for historical and seasonal trending, it can be represented as a three-dimensional cube. The number of queries becomes astronomical. This is the basis for Online Analytical Processing (OLAP), and three-dimensional tables are often referred to as [OLAP cubes].
Back in 1970, IBM invented the Structured Query Language [SQL], and today, nearly all modern relational databases support this, including IBM DB2, Informix, Microsoft SQL Server, and Oracle DB. SQL poses two challenges. First, you had to structure the data in advance to the way you expect to perform your ad-hoc queries. Deciding the groups and categories in advance can limit the way information is recorded and captured.
Second, you had to be skilled at SQL to phrase your queries correctly to retrieve the data you are after. What ended up happening was that skilled SQL programmers would develop "canned reports" with fixed SQL parameters, so that less-skilled business decision makers could base their decisions from these reports.
IBM has fully integrated stacks to help process structured data, combining servers, storage, and advanced analytics software into a complete appliance. IBM offers the [Smart Analytics System] for robust, customized deployments, and recently acquired [Netezza] for pre-configured, and more rapid deployments.
However, the bigger problem is that more than 80 percent of information is not structured!
Semi-structured data like email provides some searchable fields like From and Subject. The rest of the information is unstructured, such as text files, photographs, video and audio. To look for specific information in unstructured sources can be like looking for a needle in a haystack, and trying to get insight, patterns or trends involves text mining.
IBM is a leader in Business Analytics and has made great progress in dealing with unstructured data. This includes [IBM OmniFind Enterprise Edition], [IBM e-Discovery Manager] and [IBM Cognos Business Intelligence].
This, in effect, is what IBM Watson was able to perform so well this week. Finding the needle in the haystacks of unstructured data from 200 million pages of text stored in its system, combined with the ability to apprehend the interrelationships of meaning and subtle nuance, resulted in an impressive technology demonstration. Certainly, this new technology will be powerful for a variety of use cases across a broad set of industries!
To learn more, read the Arizona Daily Star's article [After 'Jeopardy!' win, IBM program steps out].
technorati tags: IBM, Watson, Jeopardy, Challenge, John Webster, CNET, BI, data mining, Text Mining, OLAP, Arizona, Daily Star
Continuing my rant from Monday's post [Time for a New Laptop], I got my new laptop Wednesday afternoon. I was hoping the transition would be quick, but that was not the case. Here were my initial steps prior to connecting my two laptops together for the big file transfer:
- Document what my old workstation has
Back in 2007, I wrote a blog post on how to [Separate Programs from Data]. I have since added a Linux partition for dual-boot on my ThinkPad T60.
|/dev/sda1||26GB||NTFS||C:||Windows XP SP3 operating system and programs|
|/dev/sda2||12GB||ext3||/(root)||Red Hat Enterprise Linux 5.4|
|/dev/sda6||80GB||NTFS||D:||My Documents and other data|
I also created a spreadsheet of all my tools, utilities and applications. I combined and deduplicated the list from the following sources:
- Control Panel -> Add/Remove programs
- C:\Program Files
- Start -> Programs panels
- Program taskbar at bottom of screen
The last one was critical. Over the years, I have gotten in the habit of saving those ZIP or EXE files that self-install programs into a separate directory, D:/Install-Files, so that if I had to unintsall an application, due to conflicts or compatability issues, I could re-install it without having to download them again.
So, I have a total of 134 applications, which I have put into the following rough categories:
- AV - editing and manipulating audio, video or graphics
- Files - backup, copy or manipulate disks, files and file systems
- Browser - Internet Explorer, Firefox, Opera and Google Chrome
- Communications - Lotus Notes and Lotus Sametime
- Connect - programs to connect to different Web and Wi-Fi services
- Demo - programs I demonstrate to clients at briefings
- Drivers - attach or sync to external devices, cell phones, PDAs
- Games - not much here, the basic solitaire, mindsweeper and pinball
- Help Desk - programs to diagnose, test and gather system information
- Projects - special projects like Second Life or Lego Mindstorms
- Lookup - programs to lookup information, like American Airlines TravelDesk
- Meeting - I have FIVE different webinar conferencing tools
- Office - presentations, spreadsheets and documents
- Platform - Java, Adobe Air and other application runtime environments
- Player - do I really need SIXTEEN different audio/video players?
- Printer - print drivers and printer management software
- Scanners - programs that scan for viruses, malware and adware
- Tools - calculators, configurators, sizing tools, and estimators
- Uploaders - programs to upload photos or files to various Web services
- Backup my new workstation
My new ThinkPad T410 has a dual-core i5 64-bit Intel processor, so I burned a 64-bit version of [Clonezilla LiveCD] and booted the new system with that. The new system has the following configuration:
|/dev/sda1||320GB||NTFS||C:||Windows XP SP3 operating system, programs and data|
There were only 14.4GB of data, it took 10 minutes to backup to an external USB disk. I ran it twice: first, using the option to dump the entire disk, and the second to dump the selected partition. The results were roughly the same.
- Run Workstation Setup Wizard
The Workstation Setup Wizard asks for all the pertinent location information, time zone, userid/password, needed to complete the installation.
- Re-Partition Disk Drive
I burned a 64-bit version of [System Rescue CD] and ran [Gparted] to re-partition this disk into the following:
|/dev/sda1||40GB||NTFS||C:||Windows XP SP3 operating system and programs|
|/dev/sda2||15GB||ext3||/(root)||Ubuntu Desktop 10.04 LTS|
|/dev/sda6||245GB||NTFS||D:||My Documents and other data|
- Redefine Windows directory structure
I made two small changes to connect C: to D: drive.
- Changed "My Documents" to point to D:\Documents which will move the files over from C: to D: to accomodate its new target location. See [Microsoft procedure] for details.
- Edited C:\notes\notes.ini to point to D:\notes\data to store all the local replicas of my email and databases.
- Install Ubuntu Desktop 10.04 LTS
My plan is to run Windows and Linux guests through virtualization. I decided to try out Ubuntu Desktop 10.04 LTS, affectionately known as Lucid Lynx, which can support a variety of different virtualization tools, including KVM, VirtualBox-OSE and Xen. I have two identical 15GB partitions (sda2 and sda3) that I can use to hold two different systems, or one can be a subdirectory of the other. For now, I'll leave sda3 empty.
- Take another backup of my new workstation
I took a fresh new backup of paritions (sda1, sda2, sda6) with Clonezilla.
The next step involved a cross-over Ethernet cable, which I don't have. So that will have to wait until Thursday morning.
technorati tags: IBM, Lenovo, ThinkPad, T60, T410, Intel, Clonezilla, SysRescCD, Gparted, Windows, Ubuntu, Linux, Lucid, LTS
Wrapping up my week's theme of storage optimization, I thought I would help clarify the confusion between data reduction and storage efficiency. I have seen many articles and blog posts that either use these two terms interchangeably, as if they were synonyms for each other, or as if one is merely a subset of the other.
- Data Reduction is LOSSY
By "Lossy", I mean that reducing data is an irreversible process. Details are lost, but insight is gained. In his paper, [Data Reduction Techniques", Rajana Agarwal defines this simply:
"Data reduction techniques are applied where the goal is to aggregate or amalgamate the information contained in large data sets into manageable (smaller) information nuggets."
Data reduction has been around since the 18th century.
Take for example this histogram from [SearchSoftwareQuality.com]. We have reduced ninety individual student scores, and reduced them down to just five numbers, the counts in each range. This can provide for easier comprehension and comparison with other distributions.
The process is lossy. I cannot determine or re-create an individual student's score from these five histogram values.
This next example, complements of [Michael Hardy], represents another form of data reduction known as ["linear regression analysis"]. The idea is to take a large set of data points between two variables, the x axis along the horizontal and the y axis along the vertical, and find the best line that fits. Thus the data is reduced from many points to just two, slope(a) and intercept(b), resulting in an equation of y=ax+b.
The process is lossy. I cannot determine or re-create any original data point from this slope and intercept equation.
In this last example, from [Yahoo Finance], reduces millions of stock trades to a single point per day, typically closing price, to show the overall growth trend over the course of the past year.
The process is lossy. Even if I knew the low, high and closing price of a particular stock on a particular day, I would not be able to determine or re-create the actual price paid for individual trades that occurred.
- Storage Efficiency is LOSSLESS
By contrast, there are many IT methods that can be used to store data in ways that are more efficient, without losing any of the fine detail. Here are some examples:
- Thin Provisioning: Instead of storing 30GB of data on 100GB of disk capacity, you store it on 30GB of capacity. All of the data is still there, just none of the wasteful empty space.
- Space-efficient Copy: Instead of copying every block of data from source to destination, you copy over only those blocks that have changed since the copy began. The blocks not copied are still available on the source volume, so there is no need to duplicate this data.
- Archiving and Space Management: Data can be moved out of production databases and stored elsewhere on disk or tape. Enough XML metadata is carried along so that there is no loss in the fine detail of what each row and column represent.
- Data Deduplication: The idea is simple. Find large chunks of data that contain the same exact information as an existing chunk already stored, and merely set a pointer to avoid storing the duplicate copy. This can be done in-line as data is written, or as a post-process task when things are otherwise slow and idle.
When data deduplication first came out, some lawyers were concerned that this was a "lossy" approach, that somehow documents were coming back without some of their original contents. How else can you explain storing 25PB of data on only 1PB of disk?
(In some countries, companies must retain data in their original file formats, as there is concern that converting business documents to PDF or HTML would lose some critical "metadata" information such as modificatoin dates, authorship information, underlying formulae, and so on.)
Well, the concern applies only to those data deduplication methods that calculate a hash code or fingerprint, such as EMC Centera or EMC Data Domain. If the hash code of new incoming data matches the hash code of existing data, then the new data is discarded and assumed to be identical. This is rare, and I have only read of a few occurrences of unique data being discarded in the past five years. To ensure full integrity, IBM ProtecTIER data deduplication solution and IBM N series disk systems chose instead to do full byte-for-byte comparisons.
- Compression: There are both lossy and lossless compression techniques. The lossless Lempel-Ziv algorithm is the basis for LTO-DC algorithm used in IBM's Linear Tape Open [LTO] tape drives, the Streaming Lossless Data Compression (SLDC) algorithm used in IBM's [Enterprise-class TS1130] tape drives, and the Adaptive Lossless Data Compression (ALDC) used by the IBM Information Archive for its disk pool collections.
Last month, IBM announced that it was [acquiring Storwize. It's Random Access Compression Engine (RACE) is also a lossless compression algorithm based on Lempel-Ziv. As servers write files, Storwize compresses those files and passes them on to the destination NAS device. When files are read back, Storwize retrieves and decompresses the data back to its original form.
To read independent views on IBM's acquisition, read Lauren Whitehouse (ESG) post [Remote Another Chair, Chris Mellor (The Register) article [Storwize Swallowed], or Dave Raffo (SearchStorage.com) article [IBM buys primary data compression].
As with tape, the savings from compression can vary, typically from 20 to 80 percent. In other words, 10TB of primary data could take up from 2TB to 8TB of physical space. To estimate what savings you might achieve for your mix of data types, try out the free [Storwize Predictive Modeling Tool].
So why am I making a distinction on terminology here?
Data reduction is already a well-known concept among specific industries, like High-Performance Computing (HPC) and Business Analytics. IBM has the largest marketshare in supercomputers that do data reduction for all kinds of use cases, for scientific research, weather prediction, financial projections, and decision support systems. IBM has also recently acquired a lot of companies related to Business Analytics, such as Cognos, SPSS, CoreMetrics and Unica Corp. These use data reduction on large amounts of business and marketing data to help drive new sources of revenues, provide insight for new products and services, create more focused advertising campaigns, and help understand the marketplace better.
There are certainly enough methods of reducing the quantity of storage capacity consumed, like thin provisioning, data deduplication and compression, to warrant an "umbrella term" that refers to all of them generically. I would prefer we do not "overload" the existing phrase "data reduction" but rather come up with a new phrase, such as "storage efficiency" or "capacity optimization" to refer to this category of features.
IBM is certainly quite involved in both data reduction as well as storage efficiency. If any of my readers can suggest a better phrase, please comment below.
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