Pure’s Matt Kixmoeller saw the Are SSD-based arrays a bad idea post and, unsurprisingly, responded. The SSD is Key to Economic Flash Arrays is a good post and I urge interested readers to check it out.

Pure has a stellar team with deep experience. Their views are worth considering.

As Matt notes:

This post caught our eye for an obvious reason: Pure Storage did start “fresh” to build an all-flash enterprise storage array, and we did decide to use the SSD form factor, after quite exhaustive looks at all the other options. Quite simply, we found that SSDs are the most efficient and economic building blocks from which to build a flash array. Let’s explore why.

After dismissing disk arrays that add flash drives – as I do – Matt focuses on (1) all flash appliances built from raw NAND and (2) flash arrays using flash SSDs.

SSDs are most efficient
Matt argues that SSD-based arrays have 3 key advantages:

  • Economics. SSDs are a commodity product that raw flash arrays will have a hard time out-engineering.
  • Flash controller complexity. Matt notes, correctly, that the flash controller is at the heart of argument. Better to use a controller that goes into millions of SSDs or one purpose-built for a single vendor’s array? How will the single vendor be able to keep up?
  • Servicability. Pure’s use of SSDs enables them to offer a familiar hot-swap experience that higher density designs may not offer. Futhermore, Pure’s data reduction features increase effective density to rival raw flash designs.

In conclusion, Matt makes a couple of more points. First, that SSD form factors will become much more compact, such as Apple’s DIMM-like mini-SATA SSD used in the MacBook Air. Second, that the proof is in the pudding: Pure, he says, has “. . . delivered with break-through performance, at a cost below traditional spinning disk.”

The StorageMojo take
How does Matt’s response stack up to the criteria in the original post? Not that there’s anything magic about them, but . . . .

  • Latency. No response, which doesn’t mean they’re worse.
  • SSD bandwidth. No response, but to be fair with enough SSDs you should be able saturate 16Gb Fibre Channel.
  • Reliability. No direct response. Instead a focus on servicability. More on that below.
  • Cost. Says Pure is cost-effective using their data reduction technology.
  • Flexibility. This is the heart of Matt’s argument: due to the commodity volume of the flash controllers flash SSDs will evolve faster – in functionality and cost – than any proprietary solution could. Proprietary flash controllers, he says, will be boat anchors for flash array vendors and are likely to end up controlled by flash manufacturers.

Servicability is an interesting response to the question of reliability. After all, the reason hot swap is important for some components but not others is because they either a)fail often – individually or in aggregate – b)failure compromises the product or c)online expansion, upgrading or reconfiguation is desirable.

Power supplies are routinely hot swappable because they have the lowest MTBF of any major system component. Disks are hot swappable because they come in multiples that reduce their aggregate MTBF while their standardized design makes hot swap cheap. I/O cards are often hot swappable because they are critical and needs change.

SSDs should be hot swappable because their failure rates are at best about half that of disks. But DIMMs, another critical component, especially if you invest in high-capacity ones, aren’t, because they rarely fail.

While I’m not aware of any non-SSD enterprise array vendor whose arrays don’t include hot swap components – love to be educated – which is more important: a short mean time to repair (MTTR) or a long mean time between failures (MTBF)? Because that is the argument about servicability.

I’d like to publish responses from vendors who feel strongly about this issue. Not in the comments, but as a blog post. Any takers?

Courteous comments welcome, of course. I was so impressed with the Pure Storage team that I signed a rare NDA with them last spring to get briefed, the first of 2 visits to their Castro street HQ.