Tony Pearson is a Master Inventor and Senior IT Architect for the IBM Storage product line at the
IBM Systems Client Experience Center in Tucson Arizona, and featured contributor
to IBM's developerWorks. In 2016, Tony celebrates his 30th year anniversary with IBM Storage. He is
author of the Inside System Storage series of books. This blog is for the open exchange of ideas relating to storage and storage networking hardware, software and services.
(Short URL for this blog: ibm.co/Pearson )
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Christopher Carfi on his Social Customer Manifesto blog has a great post[Let's Look at the Big Picture]that talks about Information as the new form of "money" by looking at how the concept of "money" wasfirst formed 150 years ago. Here's an excerpt:
Lesson 1: "Money" was very fragmented for a very long period of time after the colonization of North America
"Money" as we think of it in the form of cash/paper currency has only been around for about 150 years. Over a period of almost two hundred years both before and after that time, a number of fragmented methods were used to exchange value.
Lesson 2: Everybody needs to win
After the ideas of "cash" and "checks" had taken hold and become widespread, there were still many inefficiencies in the system. Cash is cumbersome, and subject to loss. Checks may bounce. This continued until the mid-1900's.
Enter the credit card.*
The credit card resonated with both customers and vendors because both parties received benefits.
Now, the widespread usage of credit cards was not something the occurred overnight. Instead, it was something that occurred over a generation. In 1970, only 16% of American households had credit cards. However, by 1995, that number had climbed to 65%.
We are now looking at Information in much the same way. It is fragmented, it is used to represent value, it is hoarded by some, shared by others. In much that "brown" is the new "black", does that mean "information" is the new"money"?
A related blog post from Shawn over at Anecdote discusses a panelist discussion of Albert Camus' work,The Stranger. Here is an excerpt:
... meaning is not pre-inscribed in the world around us and we are continuously seeking meaning in an inherently meaningless world. I almost toppled off the step machine. Do we live in an inherently meaningless world? On first thought I think the answer is yes. The onus is on us to make sense of our world.
And here is where information, by itself, is not of value unless people place value on it. Just as people valued Wampum and Furs, and could therefore trade it for other goods, people trade information for other itemsof value. But the onus is on us to make sense of the information, to determine the meaning of it, and use thisto help drive business or other accomplishments.
Are you leveraging information as well as investors leverage other people's money? If not, IBM can help.
Rather than a target weight, I chose a target waist measurement, but did not quite make this one. I did keep up with my weekly exercise regime, but we recently installed an "ice cream freezer" here at work, and I have failed to resist temptation.
Reduce, Reuse and Recycle
In my post [Stayingon Budget], I resolved to "reduce, reuse and recycle". I have taken measures to de-clutter and simplify mylife, and already things are paying off. So I am happy about this one.
Learn to Better use Lotus Notes and Office 2007 software
In my post [Honeyour Tools and Skills], I resolved to learn how to better use Lotus Notes and Office 2007. We never got Office 2007.In a surprise move, IBM put out Lotus Symphony, an Office 2007 replacement. Lotus Symphony works on IBM's three approved recognized desktop platforms (Windows XP, Linux and Mac OS X). Here's a collection of [IBM Press Releases about Lotus Symphony].
I did learn how to better use Lotus Notes,thanks to Alan Lepofsky's blog [IBM Lotus Notes Hints, Tips, and Tricks].Ironically, the best help for dealing with Lotus Notes was not the software itself, but the skills in handling emailin general. This includes:
Resist the urge to copy the world, and better use "bcc" to be kind to upper management on "reply all" respondents.
Avoid attaching large documents, but use URL's to NAS file shares, websites, or [YouSendIt.com] instead. Obviously, the recipient has to have access to whatever you point to, but it greatly reduces total email volume and improves transmission over wireless.
Delegate. A lot of times I was the "middleman" between someone asking a question, and someone else Iknew had the answer. Now, I just introduce them together and step out of the way.
Checking email only a few times a day. I use to check my email every 5-10 minutes, now only 2-4 times per day.
In my post, [Lighten Up], I resolved to laugh more, stretch more, get enough sleep, and listen to music more. I participated in monthly[Tucson Laughter Club]events, incorporated stretching in my weekly exercise program, have gotten more sleep, and rediscovered some of my older music that I hadn't listened to in a while. Overall, I feel happy I met this one.
My New Year's Resolutions for 2008:
Improve my writing skills
Going back through my past blog postings, some of my sentences and paragraphs were frightful. I resolve toimprove my sentence and paragraph structure, and make better use of HTML tags to improve the layout andformatting.
Improve my HTML and Web design skills
Contribute to the OLPC Foundation
Last year, as a "Day 1 Donor", I had donated to this important charitable organization to help educate the childrenof third world nations. This year, I plan to learn Python and other programming languages used on the XO laptop,and see how I can contribute my skills and expertise on the OLPC forums.
Eat Healthier and Drink more
I think my downfall with last year's resolution was that it was merely a goal, 35 inch waist, rather thana "call for action". This year, I plan to eat more fish, salads, whole grains and other heart-healthy foods.
While many people resolve to "Quit Drinking", I need to drink more. My doctor, my personaltrainer, and even my interpreter teams, have asked me to do so. We live in Tucson, Arizona, during a centuryof global warming, and dehydration can cause stress on the body.
Attend more movies and film-making events
Last year, I joined the Tucson Film Society, and produced[my first film], part of which was filmedfrom Bogota, Colombia. I got invited to see a lot of independent films, premieres, and film-maker events, but did not attend many. I resolve to attend more in 2008.
Get better Organized
Moving offices from one building to another brought to light that I wasn't well organized. While I havemade some efforts to de-clutter my home, I need to step this up to my work as well.
I decided to start with something very non-tech, a [Hipster PDA]. I have nowmet or heard several people who use this approach successfully, and have decided to give it a try.
Hopefully, this list might inspire you to come up with your own resolutions. Not surprisingly, writing them in a public forum helped me keep most of them, and stick to my resolutions throughout the year.
Whew! I am glad that is over. The BarryB circus has left town, he has decided to [move on to other topics], and I am now to clean up the ["circus gold"] leftbehind. I would like to remind everyone that all of these discussions have been about the architecture,not the product. IBM will come out withits own version of a product based on Nextra later in 2008, which may be different than the product that XIV currentlysells to its customers.
RAID-X does not protect against double-drive failures as well as RAID-6, but it's very close
BarryB calls this the "Elephant in the room", that RAID-6 protects better against double-drive failures. I don't dispute that. He also credits me with the term "RAID-X", but I got this directly from the XIV guys. It turns out this was already a term used among academic research circles for [distributed RAID environments]. Meanwhile, Jon Toigo feels the term RAID-X sounds like a brand of bug spray in his post[XIV Architecture: What’s Not to Like?]Perhaps IBM can change this to RAID-5.99 instead.
If you measure risk of a second drive failing during the rebuild or re-replication process ofa first drive failure, you can measure the exposure by multiplying the amount of GB at risk by thenumber of hours that the second failure could occur, resulting in a unit of "GB-hours". Here Ilist best-case rebuild times, your mileage may vary depending on whether other workloads existon the system competing for resources. Notice that 8-disk configurations of RAID-10 and RAID-5for smaller FC disk are in the triple digits, and larger SATA disk in five digits, but that with RAID-X it is only single digits. That is orders of magnitude closer to the ideal.
For each RAID type, the risk is proportional to the square of the individual drive size.Double the drive size causes the risk to be four times greater.This is not the first time this has been discussed. In [Is RAID-5 Getting Old?], Ramskovquotes NetApp's response in Robin Harris' [NetApp Weighs In On Disks]:
...protecting online data only via RAID 5 today verges on professional malpractice.
As disks get older, RAID-6 will not be able to protect against 3-drive failures. A similar chartabove could show the risk to data after the second drive fails and both rebuilds are going on,compared to the risk of a third drive failure during this time. The RAID-X scheme protects muchbetter against 3-drive failures than RAID-6.
Nothing in the Nextra architecture prevents a RAID-6, Triple-copy, or other blob-level scheme
In much the same way that EMC Centera is RAID-5 based for its blobs, there is nothing in the Nextra architecturethat prevents taking additional steps to provide even better protection, using a RAID-6 scheme, making three copiesof the data instead of two copies, or something even more advanced. The current two-copy scheme for RAID-X is betterthan all the RAID-5 and RAID-10 systems out in the marketplace today.
Mirrored Cache won't protect against Cosmic rays, but ECC detection/correction does
BarryB incorrectly states that since some implementations of cache are non-mirrored, that this implies they are unprotected against Cosmic rays. Mirroring does not protect against bit-flips unless both copies arecompared for differences. Unfortunately, even if you compared them, the best you can do is detect theyare different, there is no way of knowing which version is correct.Mirroring cache is normally done to protect uncommitted writes. Reads in cacheare expendable copies of data already written to disk, so ECC detection/correction schemes are adequateprotection. ECC is like RAID for DRAM memory. A single bit-flip can be corrected, multiple bit-flipscan be detected. In the case of detection, the cache copy is discarded and read fresh again from disk.IBM DS8000, XIV and probably most other major vendor offerings use ECC of some kind. BarryB is correctthat some cheaper entry-level and midrange offerings from other vendors might cut corners in this area.I don't doubt BarryB's assertion that the ECC method used in the EMC products may be differently implemented than theECC in the IBM DS8000, but that doesn't mean the IBM DS8000's ECC implementation is flawed.
ECC protection is important for all RAID systems that perform rebuild, and even more importantthe larger the GB-hours listed in the table above.
XIV is designed for high-utilization, not less than 50 percent
I mentioned that the typical Linux, UNIX or Windows LUN is only 30-50 percent full, and perhaps BarryBthought I was referring to the typical "XIV customer". This average is for all disk storage systems connectedto these operating systems, based on IBM market research and analyst reports. The XIV is expected to run at much higher utilization rates, and offers features like "thin provisioning" and "differential snapshot" to make this simple to implement in practice.
Most often, disks don't fail without warning. Usually, they give out temporary errors first, and then fail permanently.The XIV architecture allows for pre-emptive self-repair, initiating the re-replication process after detecting temporary errors, rather than waiting for a complete drive failure.
I had mentioned that this process used "spare capacity, not spare drives" but I was notified that there are three spare drives per system to ensure that there is enough spare capacity, so I stand corrected.
New drives don't have to match the same speed/capacity as the new drives, so three to five years from now, whenit might be hard to find a matching 500GB SATA drive anymore, you won't have to.
No RAID scheme eliminates backups or Business Continuity Planning
The XIV supports both synchronous and asynchronous disk mirroring to remote locations. Backup software willbe able to backup data from the XIV to tape. A double drive failure would require a "recovery action", eitherfrom the disk mirror, or from tape, for the few GB of data that need to be recovered.
A third alternative is to allow end-users to receive backups of their own user-generated content. For example, I have over 15,000 photos uploaded over the past six years to Kodak Photo Gallery, which I use to share with my friends and family. For about $180 US dollars, they will cut DVDs containing all of my uploaded files and send them to me, so that I do not have to worry about Kodak losing my photos.In many cases, if a company or product fails to deliver on its promises, the most you will get is your money back, but for "free services" like HotMail, FreeDrive, FlickR and others, you didn't pay anything in the first place, andthey may point this limitation of liability in the "terms of service".
XIV can be used for databases and other online transaction processing
The XIV will have FCP and iSCSI interfaces, and systems can use these to store any kind of data you want. I mentionedthat the design was intended for large volumes of unstructured digital content, but there is nothing to prevent the use of other workloads. In today's Wall Street Journal article[To Get Back Into the Storage Game, IBM Calls In an Old Foe]:
Today, XIV's Nextra system is used by Bank Leumi, a large Israeli bank, and a few other customers for traditional data-storage tasks such as recording hundreds of transactions a minute.
BarryB, thanks for calling the truce. I look forward to talking about other topics myself. These past two weeks have been exhausting!
In my post yesterday [Spreading out the Re-Replication process], fellow blogger BarryB [aka The Storage Anarchist]raises some interesting points and questions in the comments section about the new IBM XIV Nextra architecture.I answer these below not just for the benefit of my friends at EMC, but also for my own colleagues within IBM,IBM Business Partners, Analysts and clients that might have similar questions.
If RAID 5/6 makes sense on every other platform, why not so on the Web 2.0 platform?
Your attempt to justify the expense of Mirrored vs. RAID 5 makes no sense to me. Buying two drives for every one drive's worth of usable capacity is expensive, even with SATA drives. Isn't that why you offer RAID 5 and RAID 6 on the storage arrays that you sell with SATA drives?
And if RAID 5/6 makes sense on every other platform, why not so on the (extremely cost-sensitive) Web 2.0 platform? Is faster rebuild really worth the cost of 40+% more spindles? Or is the overhead of RAID 6 really too much for those low-cost commodity servers to handle.
Let's take a look at various disk configurations, for example 3TB on 750GB SATA drives:
JBOD: 4 drives
JBOD here is industry slang for "Just a Bunch of Disks" and was invented as the term for "non-RAID".Each drive would be accessible independently, at native single-drive speed, with no data protection. Puttingfour drives in a single cabinet like this provides simplicity and convenience only over four separate drivesin their own enclosures.
RAID-10: 8 drives
RAID-10 is a combination of RAID-1 (mirroring) and RAID-0 (striping). In a 4x2 configuration, data is striped across disks 1-4,then these are mirrored across to disks 5-8. You get performance improvement and protection against a singledrive failure.
RAID-5: 5 drives
This would be a 4+P configuration, where there would be four drives' worth of data scattered across fivedrives. This gives you almost the same performance improvement as RAID-10, similar protection againstsingle drive failure, but with fewer drives per usable TB capacity.
RAID-6: 6 drives
This would be a 4+2P configuration, where the first P represents linear parity, and the second represents a diagonal parity. Similar in performance improvement as RAID-5, but protects against single and double drive failures, and still better than RAID-10 in terms of drives per TB usable capacity.
For all the RAID configurations, rebuild would require a spare drive, but often spares are shared among multiple RAID ranks, not dedicated to a single rank. To this end, you often have to have several spares per I/O loop, and a different set of spares for each kind of speed and capacity. If you had a mix of 15K/73GB, 10K/146GB, and 7200/500GB drives, then you would have three sets of spares to match.
In contrast, IBM XIV's innovative RAID-X approach doesn't requireany spare drives, just spare capacity on existing drives being used to hold data. The objects can be mirroredbetween any two types of drives, so no need to match one with another.
All of these RAID levels represent some trade-off between cost, protection and performance, and IBM offers each of theseon various disk systems platforms. Calculating parity is more complicated than just mirrored copies, but this can be done with specialized chips in cache memory to minimize performance impact.IBM generally recommends RAID-5 for high-performance FC disk, and RAID-6 for slower, large capacity SATA disk.
However, the questionassumes that the drive cost is a large portion of the overall "disk system" cost. It isn't. For example,Jon Toigo discusses the cost of EMC's new AX4 disk system in his post [National Storage Rip-Off Day]:
EMC is releasing its low end Clariion AX4 SAS/SATA array with 3TB capacity for $8600. It ships with four 750GB SATA drives (which you and I could buy at list for $239 per unit). So, if the disk drives cost $956 (presumably far less for EMC), that means buyers of the EMC wares are paying about $7700 for a tin case, a controller/backplane, and a 4Gbps iSCSI or FC connector. Hmm.
Dell is offering EMC’s AX4-5 with same configuration for $13,000 adding a 24/7 warranty.
(Note: I checked these numbers. $8599 is the list price that EMC has on its own website. External 750GB drivesavailable at my local Circuit City ranged from $189 to $329 list price. I could not find anything on Dell'sown website, but found [The Register] to confirm the $13,000 with 24x7 warranty figure.)
Disk capacity is a shrinking portion of the total cost of ownership (TCO). In addition to capacity, you are paying forcache, microcode and electronics of the system itself, along with software and services that are included in the mix,and your own storage administrators to deal with configuration and management. For more on this, see [XIV storage - Low Total Cost of Ownership].
EMC Centera has been doing this exact type of blob striping and protection since 2002
As I've noted before, there's nothing "magic" about it - Centera has been employing the same type of object-level replication for years. Only EMC's engineers have figured out how to do RAID protection instead of mirroring to keep the hardware costs low while not sacrificing availability.
I agree that IBM XIV was not the first to do an object-level architecture, but it was one of the first to apply object-level technologies to the particular "use case" and "intended workload" of Web 2.0 applications.
RAID-5 based EMC Centera was designed insteadto hold fixed-content data that needed to be protected for a specific period of time, such as to meet government regulatory compliance requirements. This is data that you most likelywill never look at again unless you are hit with a lawsuit or investigation. For this reason, it is important to get it on the cheapest storage configuration as possible. Before EMC Centera, customers stored this data on WORM tape and optical media, so EMC came up with a disk-only alternative offering.IBM System Storage DR550 offers disk-level access for themost recent archives, with the ability to migrate to much less expensive tape for the long term retention. The end result is that storing on a blended disk-plus-tape solution can help reduce the cost by a factor of 5x to 7x, making RAID level discussion meaningless in this environment. For moreon this, see my post [OptimizingData Retention and Archiving].
While both the Centera and DR550 are based on SATA, neither are designed for Web 2.0 platforms.When EMC comes out with their own "me, too" version, they will probably make a similar argument.
IBM XIV Nextra is not a DS8000 replacement
Nextra is anything but Enterprise-class storage, much less a DS8000 replacement. How silly of all those folks to suggest such a thing.
I did searches on the Web and could not find anybody, other than EMC employees, who suggested that IBM XIV Nextra architecture represented a replacement for IBM System Storage DS8000. The IBM XIV press release does not mentionor imply this, and certainly nobody I know at IBM has suggested this.
The DS8000 is designed for a different "use case" andset of "intended workloads" than what the IBM XIV was designed for. The DS8000 is the most popular disk systemfor our IBM System z mainframe platform, for activities like Online Transaction Processing (OLTP) and large databases, supporting ESCON and FICON attachment to high-speed 15K RPM FC drives. Web 2.0 customers that might chooseIBM XIV Nextra for their digital content might run their financial operations or metadata search indexes on DS8000.Different storage for different purposes.
As for the opinion that this is not "enterprise class", there are a variety of definitions that refer to this phrase.Some analysts look at "price band" of units that cost over $300,000 US dollars. Other analysts define this as beingattachable to mainframe servers via ESCON or FICON. Others use the term to refer to five-nines reliability, havingless than 5 minutes downtime per year. In this regard, based on the past two years experience at 40 customer locations,I would argue that it meets this last definition, with non-disruptive upgrades, microcode updates and hot-swappable components.
By comparison, when EMC introduced its object-level Centera architecture, nobody suggested it was the replacement for their Symmetrix or CLARiiON devices. Was it supposed to be?
Given drive growth rates have slowed, improving utilization is mandatory to keep up with 60-70 percent CAGR
Look around you, Tony- all of your competitors are implementing thin provisioning specifically to drive physical utilization upwards towards 60-80%, and that's on top of RAID 5/RAID 6 storage and not RAID 1. Given that disk drive growth rates and $/GB cost savings have slowed significantly, improving utilization is mandatory just to keep up with the 60-70% CAGR of information growth.
Disk drive capacities have slowed for FC disk because much of the attention and investment has been re-directed to ATA technology. Dollar-per-GB price reduction is slowing for disks in general, as researchers are hitting physicallimitations to the amount of bits they can pack per square inch of disk media, and is now around 25 percent per year.The 60-70 percent Compound Annual Growth Rate (CAGR) is real, and can be even growing faster for Web 2.0providers. While hardware costs drop, the big ticket items to watch will be software, services and storage administrator labor costs.
To this end, IBM XIV Nextra offers thin provisioning and differential space-efficient snapshots. It is designed for 60-90 percent utilization, and can be expanded to larger capacities non-disruptively in a very scalable manner.
On his The Storage Architect blog, Chris Evans wrote [Twofor the Price of One]. He asks: why use RAID-1 compared to say a 14+2 RAID-6 configuration which would be much cheaper in terms of the disk cost? Perhpaps without realizing it, answers itwith his post today [XIV part II]:
So, as a drive fails, all drives could be copying to all drives in an attempt to ensure the recreated lost mirrors are well distributed across the subsystem. If this is true, all drives would become busy for read/writes for the rebuild time, rather than rebuild overhead being isolated to just one RAID group.
Let me try to explain. (Note: This is an oversimplification of the actual algorithm in an effortto make it more accessible to most readers, based on written materials I have been provided as partof the acquisition.)
In a typical RAID environment, say 7+P RAID-5, you might have to read 7 drives to rebuild one drive, and in the case of a 14+2 RAID-6, reading 15 drives to rebuild one drive. It turns out the performance bottleneck is the one driveto write, and today's systems can rebuild faster Fibre Channel (FC) drives at about 50-55 MB/sec, and slower ATA disk at around 40-42 MB/sec. At these rates, a 750GB SATA rebuild would take at least 5 hours.
In the IBM XIV Nextra architecture, let's say we have 100 drives. We lose drive 13, and we need to re-replicate any at-risk 1MB objects.An object is at-risk if it is the last and only remaining copy on the system. A 750GB that is 90 percent full wouldhave 700,000 or so at-risk object re-replications to manage. These can be sorted by drive. Drive 1 might have about 7000 objects that need re-replication, drive 2might have slightly more, slightly less, and so on, up to drive 100. The re-replication of objects on these other 99 drives goes through three waves.
Select 49 drives as "source volumes", and pair each randomly with a "destination volume". For example, drive 1 mapped todrive 87, drive 2 to drive 59, and so on. Initiate 49 tasks in parallel, each will re-replicate the blocks thatneed to be copied from the source volume to the destination volume.
50 volumes left.Select another 49 drives as "source volumes", and pair each with a "destination volume". For example, drive 87 mapped todrive 15, drive 59 to drive 42, and so on. Initiate 49 tasks in parallel, each will re-replicate the blocks thatneed to be copied from the source volume to the destination volume.
Only one drive left. We select the last volume as the source volume, pair it off with a random destination volume,and complete the process.
Each wave can take as little as 3-5 minutes. The actual algorithm is more complicated than this, as tasks complete early the source and volumes drives are available for re-assignment to another task, but you get the idea. XIV hasdemonstrated the entire process, identifying all at-risk objects, sorting them by drive location, randomly selectingdrive pairs, and then performing most of these tasks in parallel, can be done in 15-20 minutes. Over 40 customershave been using this architecture over the past 2 years, and by now all have probably experienced at least adrive failure to validate this methodology.
In the unlikely event that a second drive fails during this short time, only one of the 99 task fails. The other 98 tasks continue to helpprotect the data. By comparison, in a RAID-5 rebuild, no data is protected until all the blocks are copied.
As for requiring spare capacity on each drive to handle this case, the best disks in production environments aretypically only 85-90 percent full, leaving plenty of spare capacity to handle re-replication process. On average,Linux, UNIX and Windows systems tend to only fill disks 30 to 50 percent full, so the fear there is not enough sparecapacity should not be an issue.
The difference in cost between RAID-1 and RAID-5 becomes minimal as hardware gets cheaper and cheaper. For every $1 dollar you spend on storage hardware, you spend $5-$8 dollars managing the environment. As hardware gets cheaper still, it might even be worth making three copies of every 1MB object, the parallel processto perform re-replications would be the same. This could be done using policy-based management, some data gets triple-copied, and other data gets only double-copied, based on whether the user selected "premium" or "basic" service.
The beauty of this approach is that it works with 100 drives, 1000 drives, or even a million drives. Parallel processingis how supercomputers are able to perform feats of amazing mathematical computations so quickly, and how Web 2.0services like Google and Yahoo can perform web searches so quickly. Spreading the re-replication process acrossmany drives in parallel, rather than performing them serially onto a single drive, is just one of the many uniquefeatures of this new architecture.