Nimble Storage Rolls Out an All-Flash Array

As of today, there’s one more all-flash storage array on the market: Nimble Storage convened a big San Francisco shindig to roll out their own “AF” array, complete with lots of XtremIO and Pure Storage comparisons. Finally, Nimble no longer has to suffer the competitive digs and nasty rumors about this missing product, but there’s a lot more to this launch than an array sans disk!

Not Just Another All-Flash Array

Many of us in the storage industry wondered if the day would ever come that Nimble would introduce an all-flash array. What took them so long? Was there some legal impediment to them introducing an all-flash storage array? Was it some kind of internal resistance from this hybrid array standard-bearer? Or was there a technical issue?

Even after spending hours with the executives and founders of Nimble, I can’t answer those questions. But I can say that none of this matters anymore. Nimble finally has an all-flash array to sell.

Every time a company comes out with a new all-flash storage array, I fear I’ll have to point out that it’s just a regular disk array with SSDs swapped in. This criticism is inevitable when an all-flash array shares the same codebase as a disk-based storage array. Just ask NetApp (AFF), HP (3PAR), and Dell (Compellent) how often they hear this kind of jab. Then ask them to explain why it’s not fair in their case.

I must point out that Nimble’s AF series retains much of the same code from their existing hybrid arrays, so we all know what EMC (XtremIO) and Pure Storage sales reps are going to be saying. But Nimble will certainly counter that this is a proven platform with mature enterprise features and that their all-flash solution integrates seamlessly with existing disk-based arrays. Unlike the feature-light all-flash arrays from some competitors.

If they’re smart, Nimble will also point out a few novel elements of the AF series:

• The Nimble InfoSight analytics platform allowed the company to design their all-flash array based on real-world customer usage patterns
• Nimble added in-line data deduplication to the array but implemented it in a clever way that doesn’t use as much memory as competing products (more on this below)
• The familiar Nimble write sequentialization technique has been tuned for SSD, allowing them to use bigger/cheaper SSD’s without losing performance or longevity
• The Nimble approach to clustering arrays (which I’d rather call “pooling”) means you can seamlessly migrate data between all-flash and hybrid arrays

Is this just another “rip out the disks” array? I don’t think so. Nimble deserves credit for some serious engineering.

Some Cool Details About the AF Series

I spent some time with Nimble founder and VP of Engineering, Varun Mehta in an attempt to figure out what’s cool about this array. Our wide-ranging and honest discussion brought up quite a few interesting details, which I’ll try to summarize here.

It is clear that Nimble was concerned on locating the areas of technological inefficiency in storage array design. Varun pointed out that the amount of RAM available on a controller tends to limit overall array scalability, especially when data deduplication is used, and that the cost of these controllers has remained high even as the cost of NAND flash capacity has dropped dramatically. He also noted that most of the price drop for NAND is in low-end MLC, not the enterprise flash some arrays use. As Nimble set about developing an all-flash offering, they focused on optimizing the system around these limits.

Let’s start with the controllers. When designing an all-flash array, there is a temptation to cut out the SSD and try directly to integrate flash chips. After all, flash is not disk and ought to work better when treated as such. But every flash implementation needs specialized code and processors to function, not to mention physical carriers and connectors. Why not leverage the vast economies of scale by using SSD’s rather than chips directly? This is what most mainstream flash-based storage arrays do, and it’s what Nimble chose to do too.

Since flash remains fairly expensive relative to disk capacity, Nimble decided to use cheaper 3D NAND in their array. But cheaper NAND has less longevity and different performance characteristics. In an attempt to “protect” the chips in these SSD’s from excessive wear, Nimble applied a write cache and sequentialization strategy similar to the CASL concept from their hybrid arrays. Incoming writes are committed to NVRAM and then written sequentially to the SSD’s in whole blocks. Nimble believes that this will allow their 3D NAND drives to last many years longer than their competition.

One challenge for implementing data deduplication is the amount of memory it requires. The “map” of block “fingerprints” takes up quite a bit of space on every controller in the cluster. This is the main reason many all-flash arrays with inline deduplication can only support tens of terabytes of SSD. Nimble’s solution to this problem is to “page out” parts of the deduplication map to SSD and aggressively pre-fetch what is likely to be needed based on proprietary algorithms.

This is a novel approach, but it remains to be seen if it will impact performance. I can already hear the XtremIO competitive analysis folks thinking up ways to explain deterministic latency! But this trick allows Nimble to support five times the amount of storage capacity per array compared to Pure or XtremIO. For the sake of Nimble’s AF customers, I hope it works!

Nimble’s clustering approach really works to their advantage in environments with both all-flash and hybrid arrays. Unlike most symmetrical clusters, Nimble’s act as a virtualized pool. A LUN can be moved transparently between the arrays participating in the cluster, regardless of whether they are all-flash or hybrid. Clones and snapshots can also be stored on a hybrid array, where capacity costs 1/3 as much. This is a tremendous differentiator for customers, and I expect to hear a lot about it from Nimble in the coming year.

See also:

• Nimble Storage Announces Predictive Flash Platform by Dan Frith
• Nimble Storage All-Flash, late but right by Enrico Signoretti
• Nimble Storage announced their Predictive All Flash Arrays by Vipin V.K

Stephen’s Stance

It took longer than I expected for Nimble Storage to introduce an all-flash array, but their AF series looks to be a very credible offering. They’re targeting XtremIO and Pure with their marketing, but I expect HP, Dell, and especially NetApp to be cross-shopped more frequently. In that fight, I expect the Nimble AF series to be very attractive indeed!

Disclaimer: Nimble Storage flew me to San Francisco for this product launch and they’re a frequent Tech Field Day presenter. In fact, they launched the company at Tech Field Day 3 back in 2010! But no one can force me to write about them on my blog.