Disk and the new storage classification model

In my last post I explained the new storage classification that divided storage into Captive IOPS, Shared IOPS and Capacity Efficient.

Now I want to explain how disk based storage systems fit into this model.

What's interesting about disk is that you buy IOPS and get capacity for free. If you read my blog post about IOPS density, what I described was this phenomenon that disk capacities have grown so astronomically large in comparison to the IOPS that the disk provided, the effective IOPS for most of the capacity is 0.

If you are buying for IOPS then you are getting a lot of unneeded capacity. If you continue to add IOPS you are continuing to add even more excess capacity over time.

So what does that mean?

Well if you look at storage which is deployed for Captive IOPS tier, the disk capacity on the spindles deployed must be sufficient for the application. Why? Because most of the capacity is unusable because you can not drive enough IOPS through the disk. When you buy more IOPS you add more capacity, but most of the pre-existing capacity was sitting there empty anyway, so adding more capacity to a system overflowing with capacity is like adding water to the ocean.

The same holds true for the Shared IOPS tier. Namely there is a mismatch between capacity and IOPS. Each incremental increase of IOPS will result in huge increase in available but unused capacity.

What's interesting for both the Captive IOPS and Shared IOPS tier is that customers end up paying for a lot of unused capacity to get IOPS and there is no effective way to work around that.

Where disk is a really great fit is in the Capacity Efficient tier. With disk every time you add a new spindle, you are adding insignificant net new IOPS as compared to the jump in capacity. Well it turns out this is maps exactly to the economics of this tier, where the goal is to increase capacity much faster than you are adding IOPS.

And so?

I don't think disk is the new tape.

I think the economics of the Capacity Efficient tier are so very closely aligned to disk, that I have to believe that disk will continue to dominate in that tier. The Capacity Efficient tier still expects reasonable random IO performance, but is willing to endure slower performance for large increases in capacity.

Flash next...

Comments

[tim burlowski]

Thats is one of the best explanations for a tiering framework I have heard recently. I think I'll start using that when I get the question, "What kind of disk should I use?"

So tell me how backup and recovery play into that tiering?

[kostadis roussos]

Tim,

I will get to how backup and recovery fit into the story, but you'll have to wait a few posts before I get to it..

kostadis

[VJ]

Hi,

Nice to see your wonderful blogsite for netapp. lot of fundamentals able to get. Also, i would like to know, what is the general meaning of a cluster in NetApp. Because i most often hear NetApp cluster.. could you please brief me ... Thanks

[kostadis roussos]

VJ,

Thank you very much for your kind words.

As for the different flavors of cluster, you know that will make an interesting post some time later...

kostadis