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

I just read a very interesting on Computerworld.com article written by Jim Damoulakis http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9092918

Jim suggests that we’re on the verge of a “SSD Revolution” because of the significant performance advantage of Flash over disk drives. He makes several compelling and informative points regarding the pros and cons of SSD technology; however, I really wish he didn’t begin the article by discussing SSD in laptops. I believe the enterprise storage industry is missing an important distinction by making comparisons to consumer SSD products when discussing the adaptation of the technology in the enterprise. There are fundamental differences between commodity consumer-grade and enterprise-class products. Comparing consumer and enterprise flash based products is a little like comparing myself to Tiger Woods; we both play golf but, believe me, the similarities end there.

I’ve written a lot about I/O performance on this blog, and with good reason.  When I discuss Pliant’s EFD device and enterprise IT system performance issues with partners and the press, one of the questions that almost always comes up is about performance.  But, I often point out that, just like when considering a sports car, performance is only part of the equation.  Reliability is of equal importance as well.

Enterprise storage applications are demanding, and it is essential that reliability specifications are met at a 100-percent duty cycle operation on a 24/7/365 basis.  Those in the industry know that true enterprise-class disk drives are required for this environment, and that disk drives designed for low cost and low duty cycle laptop/desktop applications literally fall apart when employed in an enterprise application.  Likewise, SSDs designed for laptop/desktop applications also do not even come close to meeting the need.  So, for Enterprise Flash Drives to be accepted in the enterprise they must meet or exceed enterprise class HDD reliability. This is not a trivial task. 

The primary enterprise reliability specifications take the form of MTBF (or more meaningfully: annualized failure rate) and non-recoverable error rates (lost data).  Flash technology has three primary failure phenomenon that have a significant impact on reliability:

• Write Endurance – the limit on how many times a cell can be written/erased before it becomes damaged
• Write/Program Disturb –  writing to a given page in a Flash chip can alter bit(s) in a page that is not being written (does not damage the cell); this is sometimes referred to as “bit flip”
• Read Disturb – similar to Write Disturb, reading a page in a Flash chip can alter bit(s) in a page not being read (does not damage the cell)

A further complication is that these failure modes are not independent.  For example, the read disturb error rate is related to the number of writes or erases so that write endurance and read disturbs (and write disturbs) must be holistically considered.  It is obvious that they all contribute to non-recoverable errors, but perhaps not as obvious that they contribute to MTBF as well.  MTBF is a measurement of performance to specification, not just to some catastrophic event, as is typical with a disk drive.  This includes meeting performance and capacity specifications.

A common approach used in typical SSDs to deal with write endurance is to incorporate a wear-leveling algorithm to distribute writes across blocks within the chip(s), together with error correction (ECC), so that any damaged cells can be corrected when read.  This same ECC can then be applied for all reads to detect and correct altered bits (‘bit flips’) independently of how they became defective, i.e., write endurance, read disturb, or write disturb.  If the number of defective bits exceeds the ECC threshold, the sector(s) being read would then have to be marked as defective (non-recoverable error) and made unavailable to the system.  Depending on the amount of spare Flash capacity, at some point the resulting system capacity may well drop below the specification.

As an example, a well-known supplier of SSDs advertises an ECC that corrects up to 8 bytes in 1024 bytes, while another supplier advertises 6 bytes in 528 bytes.  At the same time, both talk about program erase/write cycles well in excess of 1 million.  However, tests show that both ECC levels would frequently result in non-recoverable errors after as few as 200,000 write/erase cycles.  These error rates result in SSD reliability falling far short of disk drive reliability in terms of non-recoverable error rate.  At the same time, overall capacity begins to erode and eventually falls below the device specification, resulting in an MTBF failure. 

And, that’s not all.  There is also a significant performance impact resulting from the management of these high error rates (It drops dramatically!).

The primary point is that enterprise-level reliability, whether it’s MTBF or non-recoverable error rate, can not be addressed with just traditional ECC.  Other techniques must be employed in addition to ECC to manage errors.  In addition, these additional techniques cannot be allowed to significantly impact performance (IOPs or bandwidth).

Sounds like a daunting task…or is it??  Stay tuned.

 Amyl Ahola

My guess is that today’s gaggle of green events, speeches and articles will focus on inspiring each of us to raise our environmental consciousness by rethinking the way we use energy.  No question, a noble and necessary exercise. 

However, one topic that I’m afraid may not receive its fair share of MSM attention is the rapidly growing problem of data center power consumption. 

Here’s the issue.  According to a recent report (http://www.energystar.gov/ia/partners/prod_development/downloads/EPA_Datacenter_Report_Congress_Final1.pdf), servers and data centers account for about 1.5 percent of all U.S. energy consumption, or 61 billion kilowatt-hours (kWh).  This is more than the electricity consumed by the nation’s color televisions in a year, and about as much energy used to power 5.8 million average U.S. households.  And, at the rate our digital information requirements are growing, server/data center energy consumption will nearly double to 100 kWh by 2011, which represents about $7.4 billion in annual electricity costs. 

So what can we do to move rapidly to greener data centers?  The worst offending part of the system, the misuse of HDDs, should be among the first to be dealt with.  The fact is that many IT managers are using 3 to 4 times more HDDs than they need from a capacity perspective just to meet growing I/O performance requirements.  This “over provisioning” does not only fail to meet I/O performance needs as I noted in earlier posts, but it’s probably one of the most inefficient uses of IT technology I’ve ever seen.  Talk about a waste of space and power (not to mention money)!

With data centers under constant pressure to operate more efficiently and reduce costs, this type of waste is ridiculous, especially when there are other viable alternatives available.  One technology that deserves serious attention is the Enterprise Flash Drive, which is based on solid state technology to offer extremely high data I/O performance. 

Here’s an example of the benefits of deploying EFDs in the enterprise, without breaking the bank.  A hybrid solution combining existing hard drives (preserving some of the initial investment) with selectively deployed EFDs can greatly enhance I/O performance while eliminating the need for HDD over-provisioning.  Best of all, this type of approach can slash data center energy consumption – up to 80 percent in some cases.

Let’s face it, enterprise data centers will continue to push the envelope in terms of performance and capacity requirements.  The trick is finding ways to meet these demands in the most efficient and cost-effective way possible, and EFDs can be a great option for many organizations.

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

Ok, I want to get back to the issue I was discussing a couple of posts ago.

The question I’m exploring is what can be done about the growing gap between disk drive and enterprise network performance, as well as the escalating inefficiencies?   One only has to look at the root cause:  the mechanical nature of disk drives.  The solution is obvious; eliminate the mechanics. 

Easier said than done! 

The Holy Grail for primary storage has always been directly addressable low latency, non-volatile random access memory.  This remains a long way off, but it is time to begin the next evolutionary step.  Solid state technology (particularly Flash) cost and performance continues to improve geometrically, and new and even more competitive semiconductor storage technologies are around the corner.  Meanwhile, disk drive performance (seek, latency) is stagnating, with only limited foreseeable improvements and with cost per I/O leveling off or even beginning to increase with time. 

Last year Greg Schulz of the StorageIO Group predicted the increasing use of solid state technology in enterprise storage applications, saying (paraphrased) that 2008 will be the year of awareness and early adoption by vendors and early deployment by customers, while 2009 will be the broader adoption phase.   Supporting that projection, EMC has recently announced their commitment to Flash and is the first major enterprise storage company to do so (http://www.emc.com/about/news/press/us/2008/011408-1.htm).  Although it was a limited announcement with what I consider an ‘entry level’ SSD technology, it is the first step towards validation of Flash technology as an enterprise primary storage device.

Solid state storage has the potential to be transformational, relegating disk drives to applications that better match their strengths, low cost per GB and large block sequential applications (for the old timers amongst us, it should be noted this is similar to the role disk played years ago with respect to magnetic tape drives).

But Flash comes with its own set of problems…(Stay tuned)

Amyl Ahola