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#1
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The State of CAS
"Malcolm Weir" wrote in message ... .... Symmetrix didn't, but Harmonix (EMC's successful AS/400 offering, perpetually overshadowed by Symm) did. My bad, then. I was involved with the early stages of the design of the precursor to what eventually I think became Harmonix (how's that for a tenuous inheritance path?) and we were planning it then - I thought based on technology that already existed in Symmetrix. On reflection, I'm not too sure about my Unisys comment, either: I'm pretty sure that Unisys used some very strange sector sizes on its disks, but not necessarily to implement redundancy checks. But other systems have at least claimed to have had them, including Sun storage and NetApp, IIRC. - bill |
#2
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Hi Bill-
Thanks for the info. I am somewhat new to the storage industry, so it sounds as though there is a lot that I could learn from you. First off, I am wondering why you claim that CAS is a marketing gimmick? The term seems to be coming more and more embraced by the industry as a whole. For instance Data Center Technologies just released a new white paper on CAS at: http://www.dacentec.com/Collateral/D...20on%20CAS.pdf Also, you are correct that CAS is dependent on immutable data. That is the whole point of CAS, providing optimal storage for fixed content data (audio, video, email, attachments, etc). In this case optimal is in terms of cost, performance, and utilization of storage capacity. Also, as you suggested, the exploding compliance market can not get enough of this technology. To clarify on the location independence of CAS objects, this really applies to writing a piece of content once, and then having that object replicated/migrated "as is" in its immutable form to multiple clusters for backup or distributed access strategies. It also applies to taking the content (as is) and migrating it through it's lifecycle to newer and newer drive technology. All of this migration is completly transparent to the application when the read request is made. Finally, the last point on authenticity. Centera is not just a WORM device, it actually guards against corrupt data that results from physical errors to the storage media. Because the data is stored based on the content address, the content address is used to authenticate the data at the point that it is read. Thus if the physical data was corrupted because of errors to the storage media, say after 8 years of residing on tape, etc with no access during that time, the data will still be authenticated based on the content address. Is this something that the other products/technologies that you mentioned also support? I appreciate your feedback and value your opinions. Thanks- Ace http://groups.yahoo.com/group/CenteraTechGroup/ |
#3
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Paul wrote in message ...
BTW, Did you ever get that porn site login you were looking for? Yes Paul, thank you very much for providing the login information. We especially enjoyed the secret home video that you provided of you and your cousin. Did she have any idea that you were filming her? You 'da man lil' Pauly!!! Talk to you soon... Ace |
#4
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#5
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"acebgur" wrote in message om... Hi Bill- Thanks for the info. I am somewhat new to the storage industry, so it sounds as though there is a lot that I could learn from you. Indeed there is. First off, I am wondering why you claim that CAS is a marketing gimmick? The term seems to be coming more and more embraced by the industry as a whole. For instance Data Center Technologies just released a new white paper on CAS at: http://www.dacentec.com/Collateral/D...20on%20CAS.pdf One of the things new entrants to the storage industy (and likely many other industries) need to learn is to distinguish between marketing and technology. If you are a salesperson, or a marketdroid, you'll likely use 'white papers' a lot: they're written for, and by, salespeople and marketdroids, they are written specifically to sell a particular product rather than to provide objective evaluations, and their technical value can be estimated accordingly. The white paper you cite above is an excellent example of this. The only *actual* CAS-specific advantage among all its verbiage is CAS's ability to collapse redundant copies of the same material (usually at the whole-file level) into a single copy - precisely the advantage I noted in my first response, and an ability which, as I noted, a file system could choose to offer as well. Every other aspect of the technology has had equivalents in file-system technology for decades (unique identifiers = inode addresses, backup overhead reduction = archive bits, distributed storage = distributed file system, content validation = additional redundancy check, etc.). And CAS can accomplish these things only after some minimal CAS awareness has been added to whatever conventional storage organization (typically, a file system) intermediates between the CAS storage and the application. If you actually want to *learn* something about storage, first acquaint yourself with the basic physical properties of disk operation (tape is already less central to most storage issues), then start reading technical journals: the annual Conference on Very Large Databases covers an incredibly wide range of relevant material, the ACM's Transactions on Database Systems does as well, and the Usenix Conference on File and Storage Technologies (FaST) may be the best place to begin your education (though the early chapters in Jim Gray's "Transaction Processing: Concepts and Techniques" are probably the best single description of soup-to-nuts storage technologies that I've ever encountered). Also, you are correct that CAS is dependent on immutable data. That is the whole point of CAS, providing optimal storage for fixed content data (audio, video, email, attachments, etc). In this case optimal is in terms of cost, performance, and utilization of storage capacity. Also, as you suggested, the exploding compliance market can not get enough of this technology. You really do sound like a marketdroid: are you sure you aren't one already? Optimal? Bull****. CAS solutions don't use any less hardware resources, are slower (because of the index look-up required to translate the file signature to the file's actual location, a stage which is not required in a conventional file system), and, as a non-standard proprietary solution, cost an arm and a leg compared to dirt-simple conventional file storage (which can easily be made robust by use of underlying RAID facilities). The market for absolutely bomb-proof reliability, via additional redundancy checks, has proven to be *very* small: modern disks are extremely good at either delivering the content that was written or returning a failure indication (allowing you to get the content from its redundant copy elsewhere), and the various interfaces and busses between them and main memory are also at least fairly reliable in this regard (I do happen to think that there's a place for additional redundancy checking in a conventional file system, at least optionally, but only because it can be done quite inexpensively: the need certainly wouldn't normally justify considering a CAS solution). And pure software solutions using conventional file storage have also been accepted for 'compliance' purposes. To clarify on the location independence of CAS objects, this really applies to writing a piece of content once, and then having that object replicated/migrated "as is" in its immutable form to multiple clusters for backup or distributed access strategies. It also applies to taking the content (as is) and migrating it through it's lifecycle to newer and newer drive technology. All of this migration is completly transparent to the application when the read request is made. Just like competent file and storage systems do. You might want to acquaint yourself with VMS clustering: it has existed since 1984, and via both shared storage and distributed host-based mirror facilities is fully capable of the functions you describe above - and supports mutable files in the process. Finally, the last point on authenticity. Centera is not just a WORM device, it actually guards against corrupt data that results from physical errors to the storage media. Because the data is stored based on the content address, the content address is used to authenticate the data at the point that it is read. Thus if the physical data was corrupted because of errors to the storage media, say after 8 years of residing on tape, etc with no access during that time, the data will still be authenticated based on the content address. Is this something that the other products/technologies that you mentioned also support? Yes: I described it in my previous response. The check is usually implemented at the block storage level rather than the whole-file level. Of course, the redundancy already present in disk and tape devices, and the busses and interfaces to them, catches virtually all such errors already without any such special checks: the worst (somewhat anecdotal) estimate I've seen for undetected end-to-end errors is on the order of 1 in 10^13 bits, and that was for PC-quality hardware quite a few years ago. - bill |
#6
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Hi Bill-
Thanks again for the info. I am wondering why some on this board are so adverse to CAS and CAS based discussions. What do you, and others, consider the "sweet spot" for messages in this group? It sounds as though you consider CAS to be nothing more than SW Voodoo that makes use of standard drive technology. Even if this is true, are you claiming that there is no value-add to be derived? And that this technology will pretty much evaporate in the very near future? To me it seems as though interest in the technology is growing at a very rapid pace. As I mentioned I am very new to the HW industry, and am coming from a SW development background. Again it sounds as CAS could be considered a SW layer that makes better use of storage space. It sounds as though you may not agree with the term "better" in this case. The point is that I am not an expert on storage, and as I mentioned previously I appreciate your feedback. You also seem to be claiming that CAS and file-systems are 2 different things. The truth is that there are companies, such as Permabit, that expose standard file systems on top of CAS managed storage devices. Also, there are several EMC Centera SW solutions that do similar things for Centera (e.g.; CAG, DX2K, StorageSwitch, etc). Finally, is this not the right group to be discussing this topic? Every time that I post something here I feel as though one of your cronies is throwing me out headfirst through the swinging saloon doors. But on the flipside 10 or 15 new members silently join the CenteraTechGroup. It is very hard to figure out. Thanks for the recomendations on research materials. Thanks! Ace http://groups.yahoo.com/group/CenteraTechGroup/ |
#7
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#8
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"acebgur" wrote in message om... Hi Bill- Thanks again for the info. I am wondering why some on this board are so adverse to CAS and CAS based discussions. I'd suggest that what they're averse (I believe that's the word you wanted) to is hype, whether of the CAS variety or any other. What do you, and others, consider the "sweet spot" for messages in this group? It sounds as though you consider CAS to be nothing more than SW Voodoo that makes use of standard drive technology. No, it's a bit less than that. Even if this is true, are you claiming that there is no value-add to be derived? In most cases, yes. In many of the rest, the value added doesn't begin to approach the added cost. And that this technology will pretty much evaporate in the very near future? I'm not in the crystall-ball-gazing business. .... You also seem to be claiming that CAS and file-systems are 2 different things. They are, though CAS duplicates one of the lower layers of a typical file system to a significant degree. The truth is that there are companies, such as Permabit, that expose standard file systems on top of CAS managed storage devices. How do they handle small updates to large files (I guess they might be able to using block-based CAS, but that's hardly fully supported across all CAS vendors)? .... But on the flipside 10 or 15 new members silently join the CenteraTechGroup. It is very hard to figure out. The phrase "There's a sucker born every minute" comes to mind. Of course, if these CAS customers are used to paying Symmetrix prices for storage, then Centera may look like a bargain to them. - bill |
#9
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#10
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In article ,
acebgur wrote: forward. When a financial institution is required to save all of their emails for 7+ years and be able to deliver/authenticate them on a moments notice, then a CAS-based product really becomes the ideal solution. Otherwise which company out there wants to save 100+ individual copies of the same 2 MB attachment for 7+ years? Why would it be necessary to do that? There are mail servers that don't keep multiple copies of identical messages and/or attachments. -- I've seen things you people can't imagine. Chimneysweeps on fire over the roofs of London. I've watched kite-strings glitter in the sun at Hyde Park Gate. All these things will be lost in time, like chalk-paintings in the rain. `-_-' Time for your nap. | Peter da Silva | Har du kramat din varg, idag? 'U` |
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