Dell EMC – What EXACTLY are you guaranteeing?

Better late than never, that was my first reaction when I learnt about the new Dell EMC Storage Efficiency Guarantee program. Then, after reading that compression, deduplication, thin provisioning, and snapshots are the features they describe as the facilitators of this program, I changed my mind. Maybe never is better?

With compression and deduplication I have no beef. Without going in to too much details on the mechanics of how they do that, these data reduction features enable allocated data to be reduced such that less physical capacity is required. In other words, they effectively increase the amount of storage capacity of the physical capacity. With all-flash storage, that’s a big deal if you want to be cost-efficient!

Thin provisioning and snapshots? That’s a different story.

Thin-provisioning is awesome for capacity planning. For example, provision a LUN with an address space of 10TB which are the projected capacity needs in three years, where the array itself is only 1TB in size. On year two buy more, if you need it. Does it save or reduce the amount of used physical capacity? No.

Snapshots are also cool for, but not limited to, saving the need to clone volumes. If you start making changes, to the original volume or to its snapshot, then you start storing only the changes. So again, a great feature that saves the user the need to create costly (capacity wise) clones. Does it save or reduce the amount of used physical capacity that is required to store the changes between the original volume and its snapshots? No.

Let’s use the data reduction tile of the Kaminario K2 GUI to see how different capacities relate to one another:

What does the 12.8:1 ratio mean? It’s the Provisioned:Physical ratio which is used for capacity planning. However, at times it might be misleading and confusing as it can be bumped up very easily. Look what happens to the data reduction tile if I provision 2500TB worth of volumes, without actually writing to them:

See how the ratio went up to 317:1? I could do the same by creating plenty of snapshots as well. You should never count on it for anything else but for capacity planning and definitely not for any type of “efficiency guarantee” as you’ll be compromising on the amount of capacity you’re actually getting. Some vendors might have different terms for their capacity types. That’s fine, just make sure any guarantee on storage efficiency is based on the following ratio:

(amount of data written to the array) : (amount of data actually stored on the array)

As my dear colleague Sundip Arora wrote in his blog, we are glad to see others in the storage industry validating the concept of guarantees. And we are confident that as customers read the fine print, figure out what really reduces data, and map what they are getting to their business needs, Kaminario’s established program will stand alone as the simplest capacity guarantee program of its kind. We are glad to finally have more points of comparison on the market.

Welcome to the party, Dell EMC.

 

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