OLTP working set known today. You don’t need hundreds of thousands of dollars of enterprise “who-ha” if a few thousand dollars will do it.

With companies like Teradata and Netezza you have to ask if doing all these things to reorganize the data for DSS (Decision Support Systems) is even necessary anymore?

mache cReeGeR: For the poor IT managers out in Des Moines struggling to get more out of their existing IT infrastructure, you’re saying that they should really look at existing vendors that supply flash caches?

steVe KLeiman: No. I actually think that flash caches are a temporary solution. If you think about the problem, caches are great with disks because there is a benefit to aggregation. If I have a lot of disks on the network, I can get a better level of performance than I could from my own single disk dedicated to me because I have more arms working for me.

With DRAM-based caches, I get a benefit to aggregation because DRAM is so expensive it’s hard to dedicate it to any single node. Neither of these is true of network-based flash caches. You can only get a fraction of performance of flash by sticking it out over the network. I think flash migrates to both sides, to the host and to the storage system. It doesn’t exist by itself in the network.

mache cReeGeR: Are there products or architectures that people can take advantage of?

steVe KLeiman: Sure. I think for the next few years, cache will be an important thing. It’s an easy way to do things. Put some SSDs (Solid State Disks) into some of the caching products, or arrays, that people have and it’s easy. There’ll be a lot of people consuming SSDs. I’m just talking about the long term.

mache cReeGeR: This increases performance overall, but what about the other issue: power consumption?

steVe KLeiman: I’m a power consumption skeptic. People do all these architectures to power things down, but the lowest-power disk is the one you don’t own. Better you should get things into their most compressed form. What we’ve seen is that if you can remove all the copies that are out in the storage system and make it only one instance, you can eliminate a lot of storage that

you would otherwise have to power.
When there are hundreds of copies of
the same set of executables, that’s a lot
of savings.
maRGo seLtzeR: You’re absolutely
right, getting rid of duplication helps
reduce power. But that’s not inconsis-
tent; it’s a different kind of power man-
agement. If you look at the cost of stor-
age it’s not just the initial cost, but also
the long-term cost, such as manage-
ment and power. Power is a huge frac-
tion, and de-duplication is one way to
cut that down. Any kind of lower-power
device, of which flash memory is one
example, is going to be increasingly
more attractive to people as power be-
comes increasingly more expensive.
steVe KLeiman: I agree. Flash can
handle a lot of the very expensive,
high-power workloads—the heavy
random I/Os. But I am working on the
assumption that disks still exist. On
a dollar-per-gigabyte basis, there’s at
least a 5-to- 1 ratio between flash and
disks, long term.
maRGo seLtzeR: If it costs five times
more to buy a flash disk than a spin-
ning disk, how long do I have to use a
flash disk before I’ve made up that 5X
cost in power savings over spinning
disk?

steVe KLeiman: It’s a fair point. Flash consumes very little power when you are not accessing it. Given the way electricity costs are rising, the cost of power and cooling over a five-year life for even a “fat” drive can approach the raw cost of the drive. That’s still not 5X. The disk folks are working on lower-power operating and idle modes that can cut the power by half or more without adding more than a few seconds latency to access. So that improves things to only 50% over the raw cost of the drive.

Look at tape-based migration systems. The penalty for making a bad decision is really bad, because you have to go find a tape, stick it in the drive, and wait a minute or two. Spinning up a disk or set of disks is almost the same since it can take longer than 30 seconds. Generally those tape systems were successful where it was expected behavior that the time to first data access might be a minute. Obviously, the classic example is backup and restore, and that’s where we see spin-down mostly used today.

If you want to apply these ideas to

general-purpose, so-called “ unstructured” data, where it’s difficult to let people know that accessing this particular data set might have a significant delay, it’s hard to get good results. By the time the required disks have all spun up, the person who tried to access an old project file or follow a search hit is on the phone to IT. With the lower-power operating modes, the time to first access is reasonable and the power savings is significant. By the way, much of the growth in data over the past few years has been in unstructured data.

eRiK RieDeL: That’s where the key solutions are going to come from. Look at what the EPA is doing with their recent proposals for Energy Star in the data center. They address a whole series of areas where you need to think about power. They have a section about the power management features you have in your device. The way that it’s likely to be written is you can get an Energy Star label if you do two of the following five things, choosing between things like de-duplication, thin provisioning, or spin-down.

But if you look at the core part of the spec, there’s a section where they’re focused on idle power. Idle power is where we have a big problem in storage. The CPU folks can idle the CPU. If there is nothing to do then it goes idle. The problem is storage systems still have to store the data and be responsive when a data request comes in. That means time-to-data and time-to-ready are important. In those cases people really do need to know about their data. The best idle power for storage systems is to turn the whole thing off, but that doesn’t give people access to their data.

We’ve never been really careful because we haven’t had to be. You could just keep spending the watts and throwing in more equipment. When you start asking “What data am I actually using and how am I using it?” you have to do prediction.

steVe KLeiman: My point is that there is so much low-hanging fruit with de-duplication, compression, and lower-power operating modes before you have to turn the disk off that we can spend the next four or five years just doing that and save much more energy than spinning it down will do.

eRiK RieDeL: We are going to have to