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.
- Pre-emptive Self-Repair
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!
technorati tags: IBM, XIV, RAID-X, RAID-5.99, RAID-5, RAID-10, RAID-6, EMC, BarryB, Risk, GB-hours, NetApp, Ramskov, Robin+Harris, StorageMojo, elephant, circus gold, Wall Street Journal, WSJ, Bank Leumi, traditional workloads, digital content, unstructured data, HotMail, FreeDrive, FlickR, KodakGallery, online, photos
Wrapping up my week's theme on IBM's acquisition XIV, we have gotten hundreds of positive articles and reviews in the press, but has caused quite a stir with the[Not-Invented-Here] folks at EMC.We've heard already from EMC bloggers [Chuck Hollis] and [Mark Twomey].The latest is fellow EMC blogger BarryB's missive [Obligatory "IBM buys XIV" Post], which piles on the "Fear, Uncertainty and Doubt" [FUD], including this excerpt here:
In a block storage device, only the host file system or database engine "knows" what's actually stored in there. So in the Nextra case that Tony has described, if even only 7,500-15,000 of the 750,000 total 1MB blobs stored on a single 750GB drive (that's "only" 1 to 2%) suddenly become inaccessible because the drive that held the backup copy also failed, the impact on a file system could be devastating. That 1MB might be in the middle of a 13MB photograph (rendering the entire photo unusable). Or it might contain dozens of little files, now vanished without a trace. Or worst yet, it could actually contain the file system metadata, which describes the names and locations of all the rest of the files in the file system. Each 1MB lost to a double drive failure could mean the loss of an enormous percentage of the files in a file system.Nothing could be further from the truth. If any disk drive module failed, the system would know exactly whichone it was, what blobs (binary large objects) were on it, and where the replicated copies of those blobs are located. In the event of a rare double-drive failure, the system would know exactly which unfortunate blobs were lost, and couldidentify them by host LUN and block address numbers, so that appropriate repair actions could be taken from remote mirrored copies or tape file backups.
And in fact, with Nextra, the impact will be across not just one, but more likely several dozens or even hundreds of file systems.
Worse still, the Nextra can't do anything to help recover the lost files.
Second, nobody is suggesting we are going to put a delicateFAT32-like Circa-1980 file system that breaks with the loss of a single block and requires tools like "fsck" to piece back together. Today's modern file systems--including Windows NTFS, Linux ext3, and AIX JFS2--are journaled and have sophisticated algorithms tohandle the loss of individual structure inode blocks. IBM has its own General Parallel File System [GPFS] and corresponding Scale out File Services[SOFS], and thus brings a lotof expertise to the table.Advanced distributed clustered file systems, like [Google File System] and Yahoo's [Hadoop project] take this one step further, recognizing that individual node and drive failures at the Petabyte-scale are inevitable.
In other words, XIV Nextra architecture is designed to eliminate or reduce recovery actions after disk failures, not make them worse. Back in 2003, when IBM introduced the new and innovative SAN Volume Controller (SVC), EMCclaimed this in-band architecture would slow down applications and "brain-damage" their EMC Symmetrix hardware.Reality has proved the opposite, SVC can improve application performance and help reduce wear-and-tear on the manageddevices. Since then, EMC acquired Kashya to offer its own in-band architecture in a product called EMC RecoverPoint, that offers some of the features that SVC offers.
If you thought fear mongering like this was unique to the IT industry, consider that 105years ago, [Edison electrocuted an elephant]. To understand this horrific event, you have to understand what was going on at the time.Thomas Edison, inventor of the light bulb, wanted to power the entire city of New York with Direct Current(DC). Nikolas Tesla proposed a different, but more appropriate architecture,called Alternating Current(AC), that had lower losses over distances required for a city as large and spread out as New York. But Thomas Edison was heavily invested in DC technology, and would lose out on royalties if ACwas adopted.In an effort to show that AC was too dangerous to have in homes and businesses, Thomas Edison held a pressconference in front of 1500 witnesses, electrocuting an elephant named Topsy with 6600 volts, and filmed the event so that it could be shown later to other audiences (Edison invented the movie camera also).
Today's nationwide electric grid would not exist without Alternating Current.We enjoy both AC for what it is best used for, and DC for what it is best used for. Both are dangerous at high voltage levels if not handled properly. The same is the case for storage architectures. Traditional high-performance disk arrays, like the IBM System Storage DS8000, will continue to be used for large mainframe applications, online transaction processing and databases. New architectures,like IBM XIV Nextra, will be used for new Web 2.0 applications, where scalability, self-tuning, self-repair,and management simplicity are the key requirements.
(Update: Dear readers, this was meant as a metaphor only, relating the concerns expressed above thatthe use of new innovative technology may result in the loss or corruption of "several dozen or even hundreds of file systems" and thus too dangerous to use, with an analogy on the use of AC electricity was too dangerous to use in homes. To clarify, EMC did not re-enact Thomas Edison's event, no animalswere hurt by EMC, and I was not trying to make political commentary about the current controversy of electrocution as amethod of capital punishment. The opinions of individual bloggers do not necessarily reflect the official positions of EMC, and I am not implying that anyone at EMC enjoys torturing animals of any size, or their positions on capital punishment in general. This is not an attack on any of the above-mentioned EMC bloggers, but rather to point out faulty logic. Children should not put foil gum wrappers in electrical sockets. BarryB and I have apologized to each other over these posts for any feelings hurt, and discussion should focus instead on the technologies and architectures.)
While EMC might try to tell people today that nobody needs unique storage architectures for Web 2.0 applications, digital media and archive data, because their existing products support SATA disk and can be used instead for these workloads, they are probably working hard behind the scenes on their own "me, too" version.And with a bit of irony, Edison's film of the elephant is available on YouTube, one of the many Web 2.0 websites we are talking about. (Out of a sense of decency, I decided not to link to it here, so don't ask)
technorati tags: IBM, XIV, EMC, BarryB, FUD, Nextra, blob, Thomas Edison, Nikolas Tesla, Web2.0, scalability, Petabyte-scale, self-tuning, self-repair, DS8000, disk, systems, Topsy, elephant, light bulb, movie camera, invention, DC, AC, YouTube[Read More]
Last week, EMC put out its press release[EMC Advances SAN Virtualization Capabilities with New Version of EMC Invista
], and fellowIBM blogger BarryW does a great job reviewing the reaction from the media, in hispost [Deja-vu - Invista 2 - again?!"
]. A few questions have popped up from my colleagues, so I thoughtI would take a stab at them here.
- Why now?
This is a reasonable question. Since Invista 2.0 came out months ago in August, and Invista 2.1 is rumored to be out by end of this month, why put out a press release now, rather than just wait a few weeks? Thesignificant part of this announcement was that EMC finally has their first customer reference.To be fair, getting a customer to agree to be a reference is difficult for any vendor. Some non-profitsand government agencies have rules against it, and some corporations just don't want to be bothered byjournalists, or take phone calls from other prospective customers. I suspect EMC wanted to put the good folks from Purdue University in front of the cameras and microphones before they:
- suffer an outage,
- change their minds, and/or
- leave for Winter break
It takes a while for new technologies to get adopted by the marketplace. Geoffrey Moore wrote a book titled [Crossing the Chasm: Marketing and Selling Disruptive Products to Mainstream Customers] that I highly recommend. If you don'thave time to read the entire book, here is a quick [11-page summary] from Parkerhill Technology Group.
In Moore's terminology, Purdue University would be a "technology enthusiast", interested in exploring the technologyof the EMC Invista. Universities by their very nature often see themselves as early adopters, willing to take big risks in hopes to reap big rewards. The chasm happens later, when there are a lot of early adopters, all willing to be reference accounts. The mainstream market--shown here as pragmatists, conservatives, and skeptics-- are unwillingto accept reference claims from early adopters, searching instead for moderate gains from minimal risks. They prefer references from customers that are similar in size and industry. Whether a vendor can get a product to cross this chasm is the focus of the book.
- Why "SAN" virtualization?
Technically, Invista is "storage" virtualization, not "SAN" virtualization. Virtualizationis any technology that makes one set of resources look and feel like a different setof resources, preferably with more desirable characteristics. You can virtualizeservers, SANs, and storage resources.
Here's a quote from Cisco's whitepaper called [Storage Virtualization a Work in Progress]
Virtual SAN (VSAN) technology, supported bythe Cisco MDS 9500 Series Multilayer Director Switch, partitions a single physical SAN into multipleVSANs, allowing different business functions and requirements to share a common physical infrastructure.
How does Invista advance Cisco's VSAN functionality? It doesn't, but that doesn't makethe title a falsehood, or the press release by association full of lies.If you read the entire press release, EMCcorrectly states that Invista is "storage" virtualization. Some storagevirtualization products, like EMC Invista and IBM System Storage SAN Volume Controller (SVC), require a SAN as a platform for which to perform their magic.Marketing people might use the term "SAN" torefer not just the network gear that provides the plumbing, but also to include the storage devices that are attached to the SAN. In that light, theuse of "SAN virtualization" can be understood in the title.
More importantly, it appears that EMC no longer requires that you purchase new SAN equipment from themwith Invista. When the Invista first came out, it cost over a quarter-million US dollars to cover thecost of the intelligent switches, but with the price drop to $100K, I imagine this means theyassume everyone has an appropriately-supported intelligent switch already deployed.
- Why this architecture?
In his post [Storage Virtualization and Invista 2.0], EMC blogger ChuckH does a fair job explaining why EMC went in this direction for Invista, and how it is different thanother storage virtualization products.
Most storage virtualization products are cache-based. The world's first disk storagevirtualization product, the IBM 3850 Mass Storage System, introduced in 1974, and thefirst tape virtualization product, the IBM 3494 Virtual tape Server, introduced in 1997, bothused disk cache in front of tape storage. Later virtualization products, like IBM SVC and HDS USP-V, use DRAM memory cache in front of disk storage, but the concept is the same.People are comfortable with cache-based solutions, because the technology is matureand well proven in the marketplace, and excited and delighted that these can offer the following features in a mixed heterogeneous disk environment:
- improved performance
- instantaneous point-in-time copy
- synchronous mirroring
- asynchronous mirroring
None of these features are provided by Invista, as there is no cache in the switch. Instead,Invista is a "packet cracker"; it cracks open each FCP packet, inspects and modifies the contents, then passes theFCP packet along to the appropriate storage device. This process slows down each read andwrite by some amount, perhaps 20 microseconds. The disadvantage of slowing down every readand write is offset by having other benefits, like non-disruptive data migration.
To compensate for Invista's inability to provide these features,EMC offers a second solution called EMC RecoverPoint, which is an in-band cache-based appliancesimilar in design to SVC, but maps all virtual disks one-to-one to physical disks. It offersremote distance asynchronous mirroring between heterogeneous devices.EMC supports RecoverPoint in front of Invista, but if you are considering buying bothto get the combined set of features, you might as well buy an IBM SVC or HDS USP-V instead,in one system, rather than two, which is much less complicated. IBM SVC and HDS USP-Vhave both "crossed the chasm" having sold thousands of units to every type and size of customer.
Hopefully, this answers the questions you might have about EMC Invista.
technorati tags: EMC, Invista, SAN, virtualization, storage, disk, systems, IBM, BarryW, Purdue, University, Geoffrey Moore, chasm, Cisco, VSAN, SAN Volume Controller, SVC, HDS, USP-V, RecoverPoint
Last year, I posted about IBM VP Bob Hoey's three[Training Videos
]about selling to the mainframe customer.
Well, his team has done it again. Here are the next three in the series:
Of course, not all of our YouTube videos are this silly. Others are focused on serious topics.Take for example this IBM UK Whiteboard session:
Wrapping up my week's theme on "Innovation that matters", I would explore how sometimes innovations are inspired by thinking differently in solving problems, and observing howothers solve similar problems in other domains.
Take for example this little Shell Oil[RealEnergy "Eureka"] video webisode. It's about eight minutes long, and helps explain a recent innovation Shellmade to help extract oil from awkward locations. Look for how the engineer was inspired by observing something his son did, that he in turn applied to innovatively solve this challenging problem.
Thinking differently has helped IBM innovate as well. Today, IBM announced it has shippped its 10,000th Storage Virtualization Engine, which coincidentally happens to correspond with today's GA date of SVC 4.2.1 release. From the [IBM Press Release]:
"IBM has been delivering virtualization capabilities for more than 40 years and today we unveil a milestone in the area of data storage virtualization with the shipment of 10,000 storage virtualization engines -- a fact no other storage company in the world can claim," said Kelly Beavers, Director, Storage Software, IBM. "By working across multiple platforms, IBM's storage virtualization helps to lower energy costs and unlocks the proprietary hold that other storage vendors have had on customers for years -- which IBM believes makes storage virtualization the killer application in the storage industry over the next decade."
SVC helps improve flexibility and responsiveness of IT infrastructures, such as creating a single virtual pool of information across the enterprise, enabling IT departments to respond more quickly to business needs and manage resources more flexibly. Benefits including increased resiliency, better application availability, simplified data migrations, and improved resource utilization can all be achieved through storage virtualization and these benefits are increased further when SVC is coupled with server virtualization such as through IBM System p LPARs and VMware ESX Server.
IBM's storage virtualization helps to unlock the proprietary hold that vendors such as EMC, HP and Hitachi have had on customers for years. With IBM SVC, customers can choose any combination of supported EMC, IBM, HP, Hitachi or other devices, virtualize them, and manage and deploy them easily and with greater flexibility and independence than ever before.
You can also read this[MarketWire] article.
I've posted before on IBM's [history of storage virtualization], but there are still a few folks not convinced.Dr. Kevin McIsaac has an article on ComputerWorld[Vendor Claims on Storage Virtualization] that warns against vendor hype. Dr. McIsaac feels"network-based storage virtualization results in a lowest common denominator view of the infrastructure, eliminating the value-added features of the array." This is really not a "network" issue, as this applies equally to Hitachi's USP-V directly cabled to external storage, no network required.IBM BarryW gives his take [Lowest Vendor Neutral Denominator] on his blog.
The concern that adding SVC (or USP-V) in front of other disk arrays adds complexity or eliminates the value-added features of older technologies, can be addressed simply by observing how similar problems were solved by the automobile industry.
- In 1911, the automobile industry introduced the "electric starter", eliminating the value-added features of the "hand crank".Instead of standing in front of the vehicle turning a hand crank over and over until the engine started, the driversat inside the vehicle and turned a small key or pressed a button, and let the "electric starter" do it. Yes, this meant thatcars were more complicated by adding a battery and electric system, but it also made cars easier to start and drive. Despite manufacturers arguing why their hand cranks were better than the hand cranks of other manufacturers, automobile models with hand cranks disappeared by 1920.
- In 1934, the automobile industry introduced the "automatic transmission" eliminating the value-added featuresof the "stick shift" and "clutch pedal". Before, people had to know when to shift gears manually, depending ontheir speed, engine RPM, and steepness of the hill they are driving on, pressing the clutch pedal at the same time, requiring skilled hand-foot coordination. Yes, cars weremore complicated with more equipment under the hood, but it made them easier and safer to drive, with one less thing to distract the driver. Surprisingly cars with automatic transmissions can be more energy-efficient, employing best practices when to automatically shift gears to optimize fuel economy.
While you can still purchase automobiles with manual transmission, the newer hybrids and electric vehiclesnearly universally all have automatic transmission. Not everyone is skilled enough to drive a car with manual transmission, something to consider when you decide which car to take on a cross-country road trip if you want to share the driving responsibilities with the rest of your group.Not surprisingly, rental car companies like Hertz offer primarily cars with automatic transmission, both forincreased safety, and to broaden the reach to all driving skill levels.
- In 1946, the automobile industry introduced "power windows", eliminating the value-added features of the window-crankon each door to roll the window up or down. Now you just press or pull a lever or button, until the window reaches the desired position. Yes, this means that cars are yet again more complicated,with little motors inside each door panel, but it made them easier to use, with the added safety option to lock out children from rolling down the back windows.
Some people actually choose manual windowsout of fear of driving their car into a lake or river, assuming a window-crank may make the difference in escaping the vehicle. It is these kinds of highly-unlikely scenarios that cause people to make bad purchase decisions. A betterapproach is to learn how to [escape from a sinking vehicle] properly, and keep the right "window-breaking" tools on hand. I keep a hammer for this purpose, and while you might think that Tucson has norivers or lakes to worry about, we do have flash floods, and I'll take knowledge-plus-hammer over window-crank any day.
So, when a company or industry innovates a new way of doing something, changing the way people think about the problem, it might take a while to take effect. SVC has been well-received in the marketplace, with thousands of delighted clients in production.
technorati tags: Shell, Oil, Eureka, video, webisode, IBM, storage, virtualization, engine, SVC, Kelly Beavers, EMC, HP, Hitachi, HDS, Kevin McIsaac, ComputerWorld, network-based, USP, USP-V, Hu Yoshida, BarryW, automobile, industry, electric starter, automatic transmission, power windows, escape, sinking, car, Tucson[Read More]