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The Storage Architect writes in his post:
Array-based replication does have drawbacks; all externalised storage becomes dependent on the virtualising array. This makes replacement potentially complex. To date, HDS have not provided tools to seamlessly migrate away from one USP to another (as far as I am aware). In addition, there's the problem of "all your eggs in one basket"; any issue with the array (e.g. physical intervention like fire, loss of power, microcode bug etc) could result in loss of access to all of your data. Consider the upgrade scenario of moving to a higher level of code; if all data was virtualised through one array, you would want to be darn sure that both the upgrade process and the new code are going to work seamlessly...
I would argue that the IBM System Storage SAN Volume Controller (SVC) is more like the HDS USP, and less like the Invista. Both SVC and USP provide a common look and feel to the application server, both provide additional cache to external disk, both are able to provide a consistent set of copy services.
IBM designed the SVC so that upgrades can occur non-disruptively. You can replace the hardware nodes, one node at a time, while the SVC system is up and running, without disruption to reading and writing data on virtual disk. You can upgrade the software, one node at a time, while the SVC system is up and running, without disruption to reading and writing data on virtual disk. You can upgrade the firmware on the managed disk arrays behind the SVC, again, without disruption to reading and writing data on virtual disk.
More importantly, SVC has the ultimate "un-do" feature. It is called "image mode". If for any reason you want to take a virtual disk out of SVC management, you migrate over to an "image mode" LUN, and then disconnect it from SVC. The "image mode" LUN can then be used directly, with all the file system data in tact.
I define "virtualization" as technology that makes one set of resources look and feel like a different set of resources with more desirable characteristics. For SVC, the more desirable characteristics include choice of multi-pathing driver, consistent copy services, improved performance, etc. For EMC Invista, the question is "more desirable for whom?" EMC Invista seems more designed to meet EMC's needs, not its customers. EMC profits greatly from its EMC PowerPath multi-pathing driver, and from its SRDF copy services, so it appears to have designed a virtualization offering that:
A post from Dan over at Architectures of Control explains the anti-social nature of public benches. City planners, in an effort to discourage homeless people from sleeping on benches in parks or sidewalks, design benches that are so uncomfortableto use, that nobody uses them. These included benches made of metal that are too hot or too cold during certainmonths, benches slanted at an angle that dump you on the ground if you lay down, or benches that have dividers sothat you must be in an upright seated position to use.
This is not a disparagement of split-path switch-based designs. Rather, EMC's specific implementation appears to be designed for it to continuevendor lock-in for its multi-pathing driver, continuevendor lock-in for its copy services when used with EMC disk, and only provide slightly improved data migration capability for heterogeneous storage environments. Other switch-based solutions, such as those from Incipient or StoreAge, had different goals in mind.
Sadly, my IBM colleague BarryW and I have probably spent more words discussing Invista than all eleven EMC bloggers combined this year. While everyone in the industry is impressed how often EMC can sell "me, too" products with an incredibly large marketing budget, EMC appears not to have set aside funds for the Invista.
If a customer could design the ideal "storage virtualization" solution that would provide them the characteristics they desire the most from storage resources, it would not be anything like an Invista. While there are pros and cons between IBM's SVC and HDS's TagmaStore offerings, the reason both IBM and HDS are the market leaders in storage virtualization is because both companies are trying to provide value to the customer, just in different ways, and with different implementations.
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When new technologies are introduced to the marketplace, it is normal for customers to be skeptical.
My sister is a mechanical engineer, so when she needs to configure a part or component, she candesign it on the computer, and then use a "Rapid Prototyping Machine"that acts like a 3D printer, to generate a plastic part that matches the specifications. Some machinesdo this by taking a hunk of plastic and cutting it down to the appropriate shape, and others use glue andpowder to assemble the piece.
But not everything is that simple. Harry Beckwith deals with the issue of selling services and software featuresin his book "Selling the Invisible". How do you sell a service before it is performed? How do you sell a softwarefeature based on new technology that the customer is not familiar with?
Our good friends over at NetApp, our technology partners for the IBM System Storage N series, developed a"storage savings estimator" tool that can provide good insight into the benefits of Advanced Single InstanceStorage (A-SIS) deduplication feature.
I decided to run the tool to analyze my own IBM Thinkpad C: drive (Windows operating system and programs) and D: drive ("My Documents" folder containing all my data files) to see how much storage savings thetool would estimate. Here are my results:
WINXP-C-07G (C: drive)Total Number of Directories: 1272Total Number of Files: 56265Total Number of Symbolic Links: 0Total Number of Hard Links: 41996Total Number of 4k Blocks: 2395884Total Number of 512b Blocks: 18944730Total Number of Blocks: 2395884Total Number of Hole Blocks: 290258Total Number of Unique Blocks: 1611792Percentage of Space Savings: 20.61Scan Start Time: Wed Sep 5 14:37:06 2007Scan End Time: Wed Sep 5 14:53:51 2007WINXP-D-07H (D: drive)Total Number of Directories: 507Total Number of Files: 7242Total Number of Symbolic Links: 0Total Number of Hard Links: 11744Total Number of 4k Blocks: 3954712Total Number of 512b Blocks: 31610595Total Number of Blocks: 3954712Total Number of Hole Blocks: 3204Total Number of Unique Blocks: 3524605Percentage of Space Savings: 10.79Scan Start Time: Wed Sep 5 14:21:16 2007Scan End Time: Wed Sep 5 14:34:30 2007
I am impressed with the results, and have a better understanding of the way A-SIS works. A-SIS looks at every4kB block of data, and creates a "fingerprint", a type of hash code of the contents. If two blocks have different "fingerprints", then the contents are known to be different. If two blocks have the same fingerprint, it is mathematically possible for them to be unique in content, so A-SIS schedules a byte-for-byte comparison to be sure they are indeed the same. This might happen hours after the block is initially written to disk, but is a much safer implementation, and does not slow down the applications writing data.
(In an effort to provide support "real time" as data was being written, earlier versions of deduplication
The estimator tool runs on any x86-based Laptop, personal computer or server, and can scan direct-attached, SAN-attached, or NAS-attached file systems. If you are a customer shopping around for deduplication, ask your IBM pre-sales technical support, storage sales rep, or IBM Business Partner to analyze your data. Tools like this can help make a simple cost-benefit analysis: the cost of licensing the A-SIS software feature versus the amount of storage savings.
technorati tags: IBM, Rapid prototyping, 3D printer, Harry Beckwith, Selling the Invisible, IBM, NetApp, Advanced Single Instance Storage, A-SIS, deduplication, fingerprint, hash code, EMC, flaw, MD5, Centera