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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.
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.
It's safer that way.
technorati tags: Seth Godin, Swedish, saying, bad, weather, clothing, snow, Tucson, coat, check, room, IBM, block-based, disk, storage, DR550, N series, NAS, healthcare, life sciences, grid, medical, archive, solution, GMAS, cont
Here's an interesting article in Raptured Monkey: Big Blue...Big Borg!
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.Read More]
I just got a series of videos made at last month's IBM Pulse 2009 conference.Rather than flood you with all of them all at once, I will post them all separately.
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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
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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.