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Why I Tire of "Tier Zero Storage"

Debunking Tier 0 Storage Babble

May 18, 2009 - by Zsolt Kerekes, editor

"Tier 0" is not a term I've ever knowingly used in editorial - which you may find strange for a storage publication which talks so much about SSDs and storage architecture.

It's not that I'm unaware of its existence. I just resist any jargon term which contributes no useful new concepts or (as is the case with tier 0) is completely misleading and doesn't tell you anything you didn't already know.

Don't get me wrong. I've got nothing against recognizing that traditional storage hierarchies need to add new levels.

I remember telling a bunch of bunch of HSM vendors back in 1999 that their pretty little pyramid shaped diagrams seemed to be lacking a level or two for SSDs.

"What's an SSD?" I was asked. OK that was 10 years ago, and they might have had an excuse for not knowing back then. The HSM companies didn't exactly set the world on fire because they were mainly backwards looking. They knew how to tell the difference between a tape drive, optical jukebox and hard disk and if you bought their software - the supplier had gone bust or acquired before you installed version 2.0. HSM stopped being a sexy term in press releases round about the same time that NAS came into vogue.

You may be surprised that as recently as a few months ago (in 2009) I was amazed by a storage vendor who was so proud of the ability of their software to help you manage the difference between 7,200 RPM and 15,000 RPM storage arrays. I asked what it could do about 300,000 RPM equivalent storage - like SSDs? "It can't do those" - I was told. I won't name the company here - because I'm not trying to embarrass anyone.

Sometimes I'll adopt a new jargon term the very 1st time I see it. A recent example of that was "write amplification".

On a slow news day I'll poke fun at companies who try to twist and chisel perfectly good words (which are understood by nearly everyone) into newer varieties, with a slight nuance of meaning. There's a list of examples on the RAID systems page if you're interested.

Green storage? - Hmpf.

Mostly when a new phrase comes along - I'll wait and see how many other companies adopt it before running with it in a big way.

So why have I resisted the term "tier 0 storage" for so many years?

What have I got against it?

My answer comes in 2 parts....

1 - What's wrong with "SSD"? - A simple word which is starting to become better understood - and is in fact the #1 search term which brings readers to this site. (OK we know that SSD is preloaded with many cultural values and assumptions - depending on who uses the word. And we also know that not all SSDs are created equal. That's a topic of many articles.)

2 - Tier 0 is misleading. It gives you a simplistic and unrealistic view of the storage acceleration concept.

Suppose you plug in a PCIe flash SSD card to a server. I think most tier 0 fans would agree that's a good example of what their beloved term is about. (Other variations can also include SSDs with other interfaces installed inside or close to the server box.) So far - so good. The result - in a well designed system - is a server which can run some applications faster than the same server using rotating storage. That's the principle I call SSD CPU equivalence. It's not a new concept BTW. Just a newish phrase for something I discovered in systems I was integrating 20 years ago - and was known to many others - long before then.

At this point.... We've successfully used an SSD and the term "tier 0" in a context which seems clear and unambiguous.

Now it will get complicated... What happens when you have 100 or so of these "tier 0" inside servers operating in an application where they have to share or exchange some critical data?

A new bottleneck creeps in - on the SAN. (I'll call it the SAN to keep it simple - but actually the storage interconnect between the 100 or so servers could be Ethernet, InfiniBand or whatever.)

As we know from hundreds of published (and more unpublished) case studies the fix to this type of problem is to attach a faster SSD (typically a RAM SSD) to unblock the dataflow logjams across the storage network.

So now we have a new box - the dataflow logjam unblocker - which may internally have a latency and bandwidth 10x or 100x faster than the SSDs - which we earlier called "Tier 0 storage".

What are we going to call the new SAN SSD? - Derrr... "Tier minus one?" or "Tier a bigger number?"

You can see my quarrel with "Tier 0". It assumes a very simple architectural model. And extrapolating from the term takes you nowhere useful from a semantic or technical point of view. It really doesn't tell you anything that you didn't already know before.

In real life you can have multiple levels of SSD at the DAS level - inside the server box - and externally too. It's going to be hard enough learning about all the many flavors of SSD. So let's not waste any of our precious brain cells by investing "tier 0 storage" with an importance it doesn't deserve.

later related articles

auto-tiering / caching SSD appliance news
7 SSD silos in the all solid state datacenter

Later:-February 22, 2010 - Tiering is Dead, Long Live Tiering - by Ron Bianchini CEO of Avere Systems says "Rather than predicting which storage tiers will win and the capacity of those tiers in a solution, the important information needed to judge a tiering solution is how the tiers are used."

February 8, 2011 - Tips to tier storage without system-controlled storage tiering - by Rick Vanover discusses what you can do manually.

See also:- Auto-tuning SSD Accelerated Pools of storage

November 8, 2011 - SSD Caching versus Tiering - by Andy Mills provides a good vantage point for seeing the many possible views of SSD tiering deployments.
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