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Tony Pearson is a Master Inventor, Senior IT Architect and Event Content Manager for [IBM Systems for IBM Systems Technical University] events. With over 30 years with IBM Systems, Tony is frequent traveler, speaking to clients at events throughout the world.
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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!
This is great news for everyone. I have said before that VMware is perhaps the best product EMC offers, and some EMC bloggers have returned the favor saying that SVC might just be the best disk system that IBM offers. While IBM and EMCare heavily competitive in other aspects of the IT storage industry, when it comes to delivering what is right for the customer, we can set aside those differences. IBM is the number one reseller of VMware, and it is a great pairing with SAN Volume Controller.
Of course, it is not a free-for-all. VMware has a few restrictions at this time:
The VMware certification is limited to Windows operating system, specifically those listed on its [Guest OS Guide].The list looks fairly extensive, so if you were running Windows guests on VMware to SVC today via RPQ,you are probably covered. However, if you are running NetWare or Linux, then the VMware certification doesnot yet apply.
host bus adapters
Only Qlogic host bus adapters are supported at this time. This is because VMware directly communicates to the host bus adapters as part of its "I/O virtualization" capabilities, and needs to work with or test with all the other HBA manufacturers.
no RDM support
Raw Device Mapping (RDM) mode is currently not yet supported. This probably will only affect a small percentage of customers, as I don't know of any major applications that require this.
Of course, most of these issues can probably be addressed with additional testing, or minor software changes, and IBM will work with VMware to prioritize what added testing or software changes are needed to expand this support.
I have created blog categories, based on our System Storage offering matrix, which you can track individually:
Disk systems, including the IBM System Storage DS Family of products, SAN Volume Controller, N series, as well as features unique to these products, such as FlashCopy, MetroMirror, or SnapLock. Tape
Tape systems, including the IBM System Storage TS Family of products, tape-related products in the Virtualization Engine portfolio, drives, libraries and even tape media.
Storage Networking offerings, from Brocade, McData, Cisco and others, such as switches, routers and directors.
Infrastructure management, including IBM TotalStorage Productivity Center software, IBM Tivoli Provisioning Manager, IBM Tivoli Intelligent Orchestrator, and IBM Tivoli Storage Process Manager.
Business Continuity, including IBM Tivoli Storage Manager, Tivoli CDP for Files, Productivity Center for Replication software component, Continuous Availability for Windows (CAW), Continuous Availability for AIX (CAA).
Lifecycle and Retention offerings, including our IBM System Storage DR550, DR550 Express, GPFS, Tivoli Storage Manager Space Management for UNIX, Tivoli Storage Manager HSM for Windows, and DFSMS.
Storage services, including consulting, assessments, design, deployment, management and outsourcing.
This week I am in Maryland, teaching at our Top Gun sales training class.
Of course, often it is the students teaching me something new. Bringing up freshnew ways at looking at things.
Take for example this new online video game called Capacity Crisis. In it, you are the storage administrator tryingto get additional storage capacity to all the different departmentmanagers that need more space.
Continuing this week's theme on Business Continuity, I will use this post to discuss this week'sIBM solid state disk announcement.This new offering provides a new way to separate programs from data, to help minimizedowntime and outages normally associated with disk drive failures.
Until now, the method most people used to minimize the amount of data on internalstorage was to use disk-less servers with Boot-Over-SAN, however, not all operating systems, and not all disk systems, supported this.
Windows, however, is not supported, because of the small 4GB size and USB protocol limitations. For Windows, you would add a SAS drive, you boot from this hard drive, and use the 4GB Flash drive for data only.
So what's new this time? Here's a quick recap of July 17 announcement. For the IBM BladeCenter HS21 XM blade servers, new models of internal "disk" storage:
Single drive model
A single 15.8GB solid-state disk drive, based on SATA protocol. In addition to theLinux operating systems mentioned above, the capacity and SATA protocols allowsyou to boot 32-bit and 64-bit versions of Windows 2003 Server R2, with plans in placeto other platforms in the future, such as VMware. I am able to run my laptop Windows with only 15GB of C: drive, separating my data to a separate D: partition, so this appears to be a reasonable size.
Dual drive model
The dual drive fits in the space of a single 2.5-inch HDD drive bay.You can combine these in either RAID 0 or RAID 1 mode.
RAID 0 gives you a total of 31.6GB, but is riskier. If you lose either drive,you lose all your data. Michael Horowitz of Cnet covers the risks of RAID zerohere andhere.However, if you are just storing your operating system and application, easily re-loadable from CD or DVD in the case of loss, then perhaps that is a reasonable risk/benefit trade-off.
RAID 1 keeps the capacity at 15.8GB, but provides added protection. If you loseeither drive, the server keeps running on the surviving drive, allowing you to schedule repair actions when convenient and appropriate. This would be the configuration I would recommend for most applications.
Until recently, solid state storage was available at a price premium only. Flash prices have dropped 50% annually while capacities have doubled. This trend is expected to continue through 2009.
According to recent studies from Google and Carnegie Mellon, hard drives fail more oftenthan expected. By one account, conventional hard disk drives internal to the server account for as much as 20-50% of component replacements.IBM analysis indicates that the replacement rate of a solid state drive on a typical blade server configuration is only about 1% per year, vs. 3% or more mentionedin the these studies for traditional disk drives.
Flash drives use non-volatile memory instead of moving parts, so less likely to break down during high external environmental stress conditions, like vibration and shock, or extreme temperature ranges (-0C° to +70°C) that would make traditional hard disks prone to failure.This is especially important for our telecommunications clients, who are always looking for solutions that are NEBS Level 3 compliant.
As with any SATA drive, performance depends on workload.Solid state drives perform best as OS boot devices, taking only a few secondslonger to boot an OS than from a traditional 73GB SAS drive. Flash drives also excel in applications featuring random read workloads, such as web servers. For random and sequential write workloads, use SAS drives instead for higher levels of performance.
Part of IBM's Project Big Green, these flash drives are very energy efficient. Thanks to sophisticated power management software, the power requirement of the solid state drive can be 95 percent better than that of a traditional 73GB hard disk drive. These 15.8GB drives use only 2W per drive versus as much as 10W per 2.5” hard drive and 16W per 3.5” hard drive. The resulting power savings can be up to 1,512 watts per server rack, with 50% heat reduction.
So, even though this is not part of the System Storage product line, I am very excitedfor IBM. To find out if this will work in your environment, go to the IBM Server Provenwebsite that lists compatability with hardware, applications and middleware, or review the latest Configuration and Options Guide (COG).
On his blog post on preparation, Seth Godin mentioned an appropriate Swedish saying:
There is no bad weather, just bad clothing.
Appropriate because it snowed here in Tucson, Arizona on Sunday evening, leaving many of us here figuring out how to drive through the stuff on Monday. In my entire lifetime, I have only witness snow down in the Tucson valley a handful of times. It got me thinking about coats, and the wonderful schemes for coat check rooms, as an analogy for data access. A lot of people ask me to compare and contrast one technology from another, say block-level virtualization from content-addressable storage, and so on, and I always try to find a good analogy to help explain things.
Let's start with the setting. It is snowing outside and people are wearing coats. When they come inside, they check their coats at a coat check room, a large room with rows and rows of racks with hangers. A coat check attendant takes your coat and puts it on a hanger, and gives you a ticket or other identifier that will allow you to retrieve your coat later. The ticket must have sufficient information to retrieve the coat quickly, rather than searching rows and rows of hangers for it.
Block-based disk storage
You walk to the coat-check desk, tell the attendant to hang your coat on a specific hanger, say hanger number 387. When you come back, you ask for the coat on hanger 387. The coat-check attendant knows exactly where hanger 387 is, and is able to retrieve it quickly. Most disk systems use this approach, including IBM SAN Volume Controller and DS family of disk systems.
Name-based disk storage
You walk to the coat-check desk, tell the person the name that you want to call your coat. An empty hanger is located, and a list of coat names, with their associated hanger number, is then kept. Upon return, you ask for your coat by name, and the coat-check attendant looks up the hanger number to match, and retrieves your coat. This is the scheme used by the IBM System Storage DR550, N series for NAS storage, and the IBM Healthcare and Life Sciences Grid Medical Archive Solution (GMAS).
Content-addressable storage (CAS)
You walk to the coat-check desk and hand them your coat. The attendant weighs your coat, checks the brand, the size, the number of buttons and zippers, types it all in, and the computer spits out a "hash code" from 1 to 99999. An empty hanger is found, and the hash code is associated to the hanger number. Upon return, you provide the hash code you were given, and the coat-check attendant looks up the hanger number to match, and retrieves your coat.This is the scheme used for some non-erasable, non-rewriteable storage, such as the EMC Centera.
IBM invented hash codes in 1953 as a way to speed up searches. For example, if you want to look up a word in the dictionary, knowing the first letter of the word makes it much quicker, because you can thumb directly to that section. A hash code was intended to give a more even distribution, so that if a million words are stored in a "hash code dictionary" then you would calculate the hash code, then look up only that section of words associated with that specific hash code number.
A problem arises when you generate "hash codes" for storage. It is possible for two different pieces of data to resolve to the same hash code. When an application tries to write a piece of data, and it resolves to a hash code that already exists, that is called a collision. One response is to either compare the incoming data to the data that is already stored, confirm they are identical, but that can be time consuming. The other response is to just assume they are identical, and reject the secondary copy, a process often referred to as "de-duplication".
What's the chance of getting a collision for data that is really different? Let's take for example the famousBirthday paradox. Suppose the coat check room assigned the hanger based on your birthday (month and day). How may coats before you run the risk of having two people turn in coats with the same birthday? After only 23 people, the likelihood is 50%. At 60 people, it goes up to 99%.
For this reason, IBM does not offer content-addressable storage. For non-erasable, non-rewriteable storage, the IBM System Storage DR550 requires the application to give each object a name, and that name is then used to storage the data, eliminating the possibility that data might accidently be thrown away.
The author is wondering whether EMC will try to avoid the fate of Hitachi's mainframebusiness, focusing on "moving into the IBM field" of offering software and services for more complete solutions.
Interestingly, one comment opines that EMC's acquisition of Documentum was "followed" byIBM's acquisition of FileNet, not realizing that IBM already has the leading documentmanagement software (IBM Content Manager).
Another comment cites IBM's recent push of Xen asanother example "following" EMC's acquisition of VMware, again not realizing that IBM has hadLogical Partition (LPAR) capability in its System z, System p and System i server lines formany years.
A few weeks ago, my Tivo(R) digital video recorder (DVR) died. All of my digital clocks in my house were flashing 12:00 so I suspect it wasa power strike while I was at the office. The only other item to die was the surge protector,and so it did what it was supposed to do, give up its own life to protect the rest of myequipment. Although somehow, it did not protect my Tivo.
I opened a problem ticket with Sony, and they sent me instructions on how to send itover to another state to get it repaired.Amusingly, the instructions included "Please make a backup of the drive contents beforesending the unit in for repair." Excuse me? How am I supposed to do that, exactly?
My model has only a single 80GB drive, and so my friend and I removed the drive and attachedit to one of our other systems to see if anything was salvageable. It failed every diagnostictest. There was just not enough to read to be usable elsewhere.
This is typical of many home systems. They are not designed for robust usage, high availability, nor any form of backup/recovery process. Some of the newer models havetwo drives in a RAID-1 mode configuration, but most have many single points of failure.
And certainly, it is not mission critical data. Life goes on without the last few episodesof Jack Bauer on "24", or the various Food Network shows that I recorded for items I planto bake some day. For the past few weeks, I have spent more time listening to the radioand reading books. Somehow, even though my television runs fine without my Tivo, watchingTV in "real time" just isn't the same.
I suspect that if you gave someone a method to do the backup, most would not bother to useit. People are now relying more and more heavily on their home-basedinformation storage systems, digital music, video and cherished photographs. Perhaps experiencing a "loss" will help them appreciate backup/recovery systems so much more than they do today.
For those of you worried about my mysterious absence on the blogosphere, I am getting better. Sorry for not posting much lately, I have had more serious issues to worry about. I am awaiting results on whether I have Dengue fever from Brazil, Avian flu from Thailand, Malaria from Kenya, or perhaps it is just food poisoning from the otherwise fabulous French cuisine I ate last week in the South Pacific. Well, I am back in town for a while, and hopefully will recover to full health, and have some time to reflect my thoughts on storage topics.
Speaking of which, a lot has happened while I was out. Let's take a quick look.
Following our introduction of the world's first encryption-capable tape drive, the TS1120, IBM now offers higher capacity 700GB cartridges, in standard 3592 format.
The DS8000 Turbo disk system now is being offered with a flexible choice of warranty periods, 1-year, 2-year, 3-year and 4-year. Since IBM was the only one to offer 4-year warranties, it was sometimes difficult to compare apples-to-apples with our competition that offered lesser warranty periods. Now, we can match the warranty period you need, so the focus can shift on the added value the DS8000 Turbo provides at the right price.
IBM's newest low-end half-high tape drive, the TS2230 Tape Drive Express Model H3L, part of our Express portfolio of offerings designed for small and medium-sized businesses (SMB). It supports the latest LTO Generation 3 specification, so fully compatible with our larger tape systems, as well as the LTO-based gear from HP and Quantum.