In a previous blog, I suggested that performance, reliability, IOPS per watt, and IOPS per $ are key storage metrics for enterprises. However, satisfying demanding enterprise needs goes far beyond the attainment of just these metrics. I/O-intensive enterprise IT applications require IOPS and bandwidth levels to be predictable and sustainable across a variety of workload requirements.

Predictable performance has traditionally been a challenge for SSDs in enterprise applications because workloads are random and indeterminate. This means that predictability requires consistent performance, independent of whether reading or writing data, as enterprise applications typically vary the read-to-write ratio between 60/40 and 90/10.  Ensuring that predictable performance is maintained while the workload changes is another example of how an Enterprise Flash Drive (EFD) offers differentiation from traditional SSDs. 

A performance comparison (IOmeter-based) between a well-publicized ‘enterprise’ SSD and the new Pliant EFD illustrates this difference.  From the chart, you can see how the ‘enterprise’ SSD(I) performance drops by over 80% as the read/write ratio changes. The Pliant EFD maintains its performance across the range from 100% reads to a 50/50 read/write ratio. This is because the Pliant EFD can read and write simultaneously to the drive and therefore offer substantially better and predictable performance for these demanding applications. Traditional SSDs and HDDs can only perform one read or write at a time. 

The bottom line: EFDs enable enterprises to achieve higher I/O performance, maintain performance predictability with changing workloads, offer higher levels of service quality, and dynamically address changing business requirements without adding additional hardware.   

I’m curious to hear what you think, so please feel free to comment.

Amyl

I have written about a new class of SSDs referred to as Enterprise Flash Drives (EFDs) many times.  But what does it take to make a true “enterprise-class” SSD drive?  With so many different SSDs targeted for the enterprise it can be difficult to tell which SSDs really qualify as EFDs, and which do not. 

So, I think a description and definition is in order. 

In the world of disk drives, enterprise-class products are distinguished from desktop and laptop products by their ability to provide superior performance and reliability.  This means that they are expected to perform flawlessly in mission critical environments.  This same requirement also holds true for enterprise SSD devices.  However, just like lower-end disk drives, SSDs designed for laptops and desktops simply can’t pass muster when expected to provide the performance and reliability required in a mission-critical enterprise environment.  There are a number of existing SSD products marketed for the enterprise, many of which are nothing more than re-packaged consumer grade (laptop) SSD technology.  In fact, many of the so-called “enterprise SSD” drives actually underperform HDDs in laptop applications…hardly what I would call enterprise class. 

Therefore, a true EFD must provide high levels of performance and reliability for flawless operation in mission critical, I/O-intensive environments.  Given the growing power and space concerns of today’s large enterprise environments, reduced energy consumption is becoming an equally important criterion for any new class of primary storage devices.  An EFD’s superior performance, energy efficiency and improved reliability allow data centers to substantially grow capacity and performance in existing installations while reducing energy needs and TCO.

Given these requirements, an Enterprise Flash Drive should, at a minimum, provide the following:

1. Superior I/O Performance – Adequate I/O performance levels to prevent bottlenecks, even during peak activity periods (generally 3-5 times greater than typical activity periods), without requiring extra hardware (i.e., cache)  while providing ample scalability for growth.  At a minimum, an EFD should deliver at least 100,000 random IOPS or more and be able to sustain this rate for typical block sizes (4K bytes or more). 
2. Exceptional Reliability – EFDs need to deliver significantly lower failure rates than disk drives, given the inherent benefit of solid state technology (no moving parts).  Performance and reliability must be predictable and sustainable at 100 percent duty cycles (24/7/365) without cycle-stealing maintenance or “housekeeping” actions.  Lifetime should exceed five years without performance or capacity degradation.  Robust reliability monitoring and reporting capabilities are essential.
3. Energy Efficiency – EFDs should meet new standards for green data center excellence of greater than 20,000 IOPS per Watt, with activity-based power management to limit energy consumption when the device is less than 100 percent utilized.
4. Cost Efficiency – Transaction costs ($/IOPS) must be substantially reduced from that of an HDD (<10%).  And, it goes without saying that an EFD must be form factor and interface compatible with HDDs (while providing similar storage capacities).

While these requirements are very demanding, I believe they only begin to define the needs and ability of solid state technology to transform future system and storage architectures.  In my opinion, the vast majority of today’s SSD products are already falling short of the true needs. 

Interested to hear what you think…

Amyl Ahola

Who could ask for more than seeing a new storage industry product announcement to highlight the points you’ve been trying to make?
 
I found myself in that position, and was quite surprised (well not really surprised…more like incredulous) to see a recent announcement of what had been frequently referred to as the Seagate “brick” project (not related to MiniScribe), but minimally disguised within a Seagate-funded private company.  The product that was announced is another version of a sealed unit consisting of multiple hard drives “purpose-built to maximize performance and reliability.”  The announcement makes it clear that many new techniques must have been employed to achieve “self-healing,” and to enable the product to essentially repair itself in place “to the equivalent of a fresh, factory-manufactured drive.”  Wow!  I will leave it up to people smarter than me to respond to this.

What I’d like to discuss is the price performance aspect of this announcement.  The systems tested were fully mirrored, making comparisons never quite “apples to apples.”  However, one needs to keep in mind that the MTBF of the drives employed require mirroring to reach any reasonable reliability level.  While I could not find any real price or performance data on the company’s web site, the reference to their SPC benchmarks provided considerable data.
 
From a pricing standpoint, the 1.03TB configuration sells for more than $36 per gigabyte (after a 40% discount from $60/GB)…and, flash-based SSD at $30/GB is considered expensive?
 
This benchmark is also said to be record-breaking with the lowest cost per SPC-1 IOPs.  I’m not suggesting that $36/GB is unreasonable, only that it illustrates the true cost of hard drives in high-performance environments.  A closer look at the benchmark is even more telling.  This “record-breaking” performance correlates to a response time of nearly 30 milliseconds.  In fact, response time increases dramatically starting at about 50% of the max IOPs, which is certainly troublesome for high transaction-rate systems.

This project was started a few years ago, apparently to address the growing price, performance and reliability gap in enterprise applications, as we have been talking about, and to hold off the encroachment of solid state storage devices.  However, with today’s technology, well designed Enterprise Flash Drives will not only be lower in cost per GB, less than 1/4th the cost per IOP, and more reliable.  And, did I mention power:  EFD’s will be well less than 1/100th the watts per IOPs.  I cannot help but be reminded of the Anderson Cooper segment on CNN:  “What were they thinking!”

Amyl Ahola

The dramatic reductions in HDD cost per GB have resulted in many system/storage architects (and application/operating system programmers) treating primary storage as though it is free.

Some of the results are:

• Exponential increases in the size of operating systems and applications
• Mass deployment of low-end and midrange servers with multiple copies of data (and applications)
• Over-provisioning of storage to satisfy future needs projections (which also likely adopt the concept of free storage)
• Adoption of power-hungry DRAM cache appliances to mask HDD performance shortfalls
• Over-provisioning of HDDs to mask HDD performance shortfalls

These all result in inefficient use of storage that has many costs, not the least of which is the increasing cost of energy consumption.  Some of the energy data becoming available paints a sobering picture:

• Data centers account for 1.5% of ALL U.S. electrical consumption, and this is expected to double in a few years
• Power consumption per $1,000 of server spending has increased by a factor of 4 since 2000
• Power failure and availability is expected to halt data center operations at more than 90% of all companies over the next few years
• Fifty percent of current data centers will have insufficient power and cooling capacity this year

HDDs are clearly not the only contributor to the rapid acceleration of data center power consumption, but their inefficient use is likely one of the largest contributors.  Data that suggests more than one third of data center power consumption is storage related.

Trends and techniques such as consolidation, virtualization and thin provisioning should all contribute to improved efficiencies.  But while doing so, these approaches will put increased performance demands on the HDDs.  The result:  an increased need for higher performance (i.e., higher RPM……read that as ‘power consuming’) drives and even further over-provisioning for performance – and therefore once again increased energy consumption.

It’s time for new metrics to be considered in the data centers, which take into account energy usage to aid the system designers as they optimize their systems.  Several metrics are identified at the www.greendatastorage.com website; examples cited include activity per watt, such as transactions/Watt, IOPs/Watt, and bandwidth/Watt.

I believe that Enterprise Flash Drives (EFDs) will play a major role in reversing these trends. EFDs can provide over 1000x improvement in IOPs/Watt, and an order of magnitude or more improvement in bandwidth/Watt over the highest performing HDD’s.

Amyl Ahola

I have decided to depart from my planned comments because I can’t help but mention a recent storage announcement to help make the point of how far one can go to try and overcome HDD shortfalls.  The announcement references an array of small form factor drives (2 ½”) configured to achieve a very high ‘Actuator Density’ array — a noble objective.  According to the company’s white paper, the unit is sealed and contains 160 or more drives in a 3RU rack.  The drives apparently counter rotate and are offset from each other to overcome shock and vibration issues.

The white paper also talks about 160 drives plus 10 spares in this sealed unit with a three-year minimum life, resulting from the ‘Failure in Place’ ability to dynamically swap failed drives with self-contained spare drives.  Using their own MTBF data and typical failure statistics, this configuration would result in more than 10 failures in a three-year period in more than 50 percent of the installations.  Putting this in perspective:  more than 10 failures means replacing the entire sealed unit, and in the best case, requiring many hours recovering tens-of-TBs of data.  I would not want their warranty bill!

Given the actual failure rate of HDDs (especially consumer grade HDDs used in high duty cycle environments), and not the inflated specification numbers from HDD suppliers, I can’t imagine anyone who has experienced a catastrophic HDD failure event willing to take the risk on such a ‘sealed’ configuration that doesn’t allow hot swaps.  This seems to be marketing 101 at its best:  if you have a downside, feature it!

The white paper also propositions improvements in performance and power that, at least in this author’s opinion, when subjected to similar tests of objective analysis do not hold up.

My point is not to throw stones at this particular approach, but rather use it to illustrate the magnitude of the challenge in overcoming the inherent performance and reliability shortcomings of HDDs.  When the fundamental problem is the mechanical nature of the beast, the solution is not to keep adding more of the same. 

In one sense, this is not all that different from the political discussions of the day…the question boils down to, do you want more of the same or is it time for a new paradigm?

Amyl Ahola