Acopia, one of the new super-NAS suppliers (clustering, global namespace, etc) has added a new tier to its tiered disk storage - RAM. It's managed by Acopia's ARX file virtualisation software as 'just another disk tier' only it is not. It is a server with 32GB of RAM and it functions like a RAM cache. Files with the fastest access requirements are placed in it and served to applications at memory rather than disk speed. It's a logical enough idea.

I expect it's a good way of competing with Isilon. "Okay", we might imagine the Acopia strategists thinking, "So you can serve files lightning quick from disk. Well try this one on for size and, hopefully, eat your heart out."

However fast Isilon get files off disk no disk will ever beat RAM access speed. Taneja Group analyst Brad O'Neil wrote about the idea recently in SearchStorage.

This is like using Information Lifecycle Management (ILM) concepts to accelerate data access instead of the usual ILM choir singing off the songsheet entitled 'SATA arrays: how to cut costs and have users not notice.' RAM cache embedded in the file virtualisation set up is a performance optimising technique that ought to be a lot cheaper than TMS' Ramsan and other supplier's solid state disks.

Acopia has this to say about performance and cost advantages: "In Acopia laboratory tests, when a specific application file set was served from Tier 0, the application throughput increased by almost 30 times compared to similar tests run with the same file set residing on a popular modern NAS system. Amazingly, the Tier 0 storage pool created for the test consisted solely of a single off-the-shelf server configured with 32GB memory and dual Intel processors. The cost of this configuration was under $10,000. Given the cost difference between the popular NAS system and the Tier 0 storage pool, the Tier 0 enabled solution was 300x more cost effective than the popular NAS system alone when serving this workload."

In a way this approach reminds me of Sun's Thumper which adds a thumping great lot of disk storage to a server with Opteron CPUs. Acopia is taking a similarly imaginative approach by configuring an industry-standard server with lots of RAM, little disk and saying it's just a great big cache but at the same time, unlike a NAS cache, it's a separate tier in its NAS infrastructure. Neat.

What's to stop other tiered NAS suppliers doing it? Not a lot. Add in a RAM-heavy Intel server and extend your software to treat it as a quasi-disk tier with file moving software to load it and refresh it. That should only take three months.

Let's see if other people bring out tier zero additions to their super-NAS products in the first quarter of 2007.