Now EMC’s Chuck Hollis has (bravely) stuck his neck out to try to actually compare the capacity efficiency three storage arrays in a realistic way. Good luck, Chuck! I can hear the knives sharpening over at NetApp and HP already!

Why This is a Good Idea

In all seriousness, this is exactly the sort of analysis that customers ought to be taking on. Buying a new storage device? Spec out how you want to use it and ask for proposals from vendors that are configured according to recommended practice. That’s the only way to really compare two devices: Real usable configurations.

It’s not realistic to expect that an EMC array with the same capacity and number of disks as a supposedly similar device is going to give you the same usable space, performance, energy efficiency, manageability, or really anything else. Despite the basic architectural similarities of, say, a CLARiiON and an EVA, there are just too many critical differences to think of them as a pair of apples, even if you strive for the same specs.

In fact, there are no apples or oranges anymore. No one uses straight textbook RAID. No one makes a pure NAS filer or Fibre Channel array or anything. They’ve all evolved away from the basics we think we understand, adding in a little midrange, a dash of green, and a dollop of iSCSI to become a field of grapples, tangelos, limequats, and pluots.

Why EMC Shouldn’t Be Doing It

All that being said, I think it’s beyond perilous for a vendor to try to set up a standardized comparison of capacity, just like it is foolish to try to get some kind of meaningful performance statistic between such diverse platforms.

Even when (as appears to be the case here) a vendor tries to follow their competitors’ recommendations, they’ll likely not end up with the same configuration that an experienced Systems Engineer from that company would put together. Often, these smart guys know the real-world implications of the system and can put together a system that matches the requirements better.

Regarding EMC’s specific comparison, I do have some questions, however:

1. Does EMC really support using the five vault reserve disks on a CLARiiON to hold production data? EMC SE’s have suggested to me in the past that this is a bad idea…
2. Would EMC really suggest 8+1 RAID 5 for a production Exchange and SQL Server environment?
3. Is one hot spare per two DAEs (30 drives) really sufficient for a whole pile of 9-disk RAID 5 sets that are maxed-out with production data? I’d feel much more comfortable with a few more spares with such large RAID 5 sets.
4. There is no way 14+2 RAID DP is equivalent to 4+1 RAID 5, let alone 8+1. It’s in a different league of reliability.
5. Yeah, NetApp’s space reserve recommendation stinks. But you probably won’t need 100% in production – the real amount is something one would work out when testing and piloting and is probably substantially less than this.

I’m not trying to get into an argument about this, mind, just noting a few items that immediately jumped out at me. And if I could see these five issues in my quick read, I can just imaging what HP and NetApp will see! Watch out for the knives, Chuck! I know you mean well, but exercises like this just won’t ever work.

And where are HDS, Sun, and IBM? Plus, I would love to see 3PAR, Compellent, Dell/EqualLogic, LeftHand, and the rest jump in with their numbers! Maybe I should set up a sham RFP and ask the vendors to respond with their own systems for some real comparison!

(This post was updated for clarification and to add that last suggestion…)

© sfoskett for Stephen Foskett, Pack Rat, 2008. | Grapples and Tangelos: Why it’s Impossible to Compare Fairly
This post was categorized as Enterprise storage. Each of my categories has its own feed if you'd like to filter out or focus on posts like this.