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Do you ever get the impression that to most of the storage industry the answer to all of your storage questions is “Disk!”
Two of the buzzes at SHARE during the week of August 11, 2008, were “green” from the mainframe perspective and “no more mainframe tape” from some of the disk storage vendors. These two themes seem to be in conflict with each other to me. I understand from a mainframe perspective the green theme as I was with IBM in 2003 when the mainframe group began touting the green theme of consolidation as a result of all the rolling blackouts in the State of California.
But I don't understand how the green theme and “no more mainframe tape” support one another. But let me think through this concept and I will look at it through the lens of storage tiers.
When your data are first created, it logically belong on primary storage – primary disk. I believe we all are in agreement on this point. When the data has not been referenced in over 30 days, migrate it to less expensive, and likely less reliable, disk. This is where I will start to diverge with the “disk is the answer all storage questions” philosophy. But I will not digress on this point.
When your data has not been referenced in over 90 days, migrate it again to another disk technology – maybe MAID (Massive Array of Idle Disk) – and keep it there forever and to be on the safe side, replicate each disk storage tier on more disk.
Longevity
Another point you need to be aware in all of this is that disk will likely be replaced every 3 to 5 years. So now there is a data migration effort required on your part for each disk storage tier every 3 to 5 years (compared to 10+ years on tape). And what do you get out of this data migration? The latest and greatest disk technology for each disk storage tier, a huge bill for all that new disk, maybe a services bill for the help you need to migrate your data, and time and energy from your limited personnel pool.
Energy Savings
Okay, so you think this may work because the disk-only vendors are touting that the total cost of ownership over 5 years for disk and tape are converging. Well that is not happening based on the Clipper Notes report that I referenced in my August 11, 2008 blog where the 5 year TCO for disk is about 23x that of tape and the energy cost for disk is about 290x that of tape.
You may say that study is flawed but do you think the spinning disk will cost less from an energy perspective than tape? I do not believe any of us will believe that point but MAID technology should fill that gap. Right? Well the energy requirements of MAID from the studies I have seen are still significantly higher than that of tape, almost 17x.
So why won't MAID save you that much energy? Likely because data is striped across multiple disks as a result of RAID (Redundant Array of Independent Disk) technology. Oh! That means that the striped data on the MAID devices will have to wake up all the disk that the file is striped across – not just one. So MAID needs to access more than just one disk – no big deal right?
Availability
From my mainframe days, I was informed by engineers that electrical components are more likely to fail during a power up than when they are in constant use. So to me that means the risk is greater on MAID technology as it is powered up and down often.
Restore
Now, what if you need a large file for a regulatory compliance request but that data and that disk has not be accessed for over three years. In the example above, you will retrieved your data from the MAID disk. The disks across which this file has been stripped begin to power up. You are fortunate this time as all of the disk power up without a failure. Now what about the data integrity? You are again fortunate this time as all of your data is retrieved without any double or triple bit errors. You finally get your data on primary storage because it will need to be researched for the required information for a few weeks. After your research is complete and you have satisfied your compliance request the data begins its journey down disk pool lane again.
So bringing this together, I do not see “no mainframe tape” as a green alternative. In fact, I see it as quite the opposite. So what is my solution? Use the storage tier infrastructure that has worked well in mainframe environment for decades and is becoming more prevalent in open environments. Also, be sure your data is on the appropriate tier for the appropriate amount of time for your business. What you will receive is a smaller storage bill, greater reliability from your storage tiers, and significantly lower energy bills – becoming more green!
You can read more about the benefits of storage tiers and going green in my news alert “How Much is Your Green?”
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