Client SSDs

Comparing Wear Figures on SSDs

DWPD TBW GB/Day TriangleI have been receiving questions lately from people who are puzzled when companies use different parameters than their competitors use to specify the endurance of their SSDs.  How do you compare one against the other?  Some companies even switch from one parameter to another to define the endurance of different SSDs within their product line.

I have found that Intel uses three different endurance measures for its products: DWPD (drive writes per day), TBW (terabytes written), and GB/day.

There’s not any real difference between any of these measures – each one is one way of stating how many times each of the SSD’s locations can be overwritten before the drive has gone past its warrantied life.

The relationships between these three measures are illustrated in this post’s graphic.  You can click on it to see an expanded version.  It’s all pretty simple.  We’ll spell out the relationships in detail below, but in brief, if you want to compare Continue reading

Intel Pits Optane SSDs Against NAND SSDs

Intel's Optane PyramidOnly a week after announcing its Optane Enterprise SSDs Intel has launched m.2-format Optane SSDs for end users.  It appears that we are at the onset of an Optane surge.

These SSDs communicate over the PCIe bus bringing more of the 3D XPoint’s performance to the user than would a SATA interface.

Pricing is $44 for a 16GB module and $77 for 32GB.  That’s $2.75 and $2.40 (respectively) per gigabyte, or about half the price of DRAM.  Intel says that these products will ship on April 24.

What’s most interesting about Intel’s Optane pitch is that the company appears to be telling the world that SSDs are no longer important with its use of the slogan: “Get the speed, keep the capacity.” This message is designed to directly address the quandary that faces PC buyers when considering an SSD: Do they want an SSD’s speed so much that they are willing to accept either Continue reading

Managing SSDs Using Machine Learning

Focusrite Recoring Console - photo by JacoTenSSDs use a huge number of internal parameters to achieve a tricky balance between performance, wear, and cost.  The SSD Guy likes to compare this to a recording studio console like the one in this post’s graphic to emphasize just how tricky it is for SSD designers to find the right balance.  Imagine trying to manage all of those knobs!  (The picture is JacoTen’s Wikipedia photo of a Focusrite console.)

Vendors who produce differentiated SSDs pride themselves in their ability to fine-tune these parameters to achieve better performance or endurance than competing products.

About a year ago I suggested to the folks at NVMdurance that they might consider applying their machine learning algorithm to this problem.  (The original NVMdurance product line was described in a Memory Guy post a while ago.)  After all, the company makes a machine learning engine that tunes the numerous internal parameters of a NAND flash chip to extend the chip’s life while maintaining the specified performance.  SSD management would be a natural use of machine learning since both SSDs and NAND flash chips currently use difficult and time-consuming manual processes to find the best mix of parameters to drive the design.

Little did I know that NVMdurance’s researchers Continue reading

Why 3D XPoint SSDs Will Be Slow

SNIA: Sources of SSD LatencySomething that has been confusing a number of people is the performance of Intel’s 3D XPoint-based SSDs.  Why are they so slow?

Let me back up a little – they’re not really slow.  When Intel compared its standard NAND flash based PCIe SSD to a similar SSD based on 3D XPoint memory, the XPoint model ran 7-8 times faster, which is very impressive.  Intel demonstrated that at the Intel Developer Forum (IDF) last August and several times since then.

But Intel and Micron have been boasting since its introduction that 3D XPoint Memory is 1,000 times as fast as NAND flash.  How do you get from a 1,000 times speed advantage down to a speed improvement of only 7-8 times?

That’s what the graphic in this post will explain.  The small rendition above is just Continue reading

Why SSD and HDD Prices Move in Parallel

ASTC 2016 HDD RoadmapWhy are HDD prices tracking SSD prices?  Why don’t they cross over?  These are questions that The SSD Guy is often asked, especially by people who anticipate a crossover in the near future.

In essence it’s because both the HDD industry and the semiconductor industry have set goals for themselves to achieve 30% average annual price reductions.  If they are both on the same trajectory, and if there’s an order of magnitude difference between HDD and SSD prices today, then there will be an order of magnitude difference in the future as well.

The 30% average annual decline in SSD prices has a convenient name: Moore’s Law.  Although there’s no physical, economic, or other restriction behind Moore’s Law (so it’s not really a law at all) it serves as a guide for the industry.  Chip makers set their sights at doubling the number of transistors on a chip every couple of years, and this equates to average annual price decreases of 30%.

The HDD business also Continue reading

Toshiba Reveals Restructuring Plans

Toshiba's Yokkaichi Manufacturing ComplexOn Friday Toshiba revealed its restructuring plans aimed at returning the company to profitability and growth through management accountability.

Of special interest to The SSD Guy was the fact that the company will refocus its semiconductor and HDD businesses, currently called the “Semiconductor & Storage Products Company” partly by giving it a new name: “Storage & Electron Devices Company”.  This division will focus on the semiconductor group’s good prospects and profitability while maintaining a focus on the fact that SSDs and HDDs share a business.  In the not-too-distant past Toshiba has run these two businesses separately.

The group plans to be “A pillar of income with Memories as a core business”.  To achieve this, Toshiba has stated that it will enhance its NAND cost competitiveness by accelerating development of BiCS (Toshiba’s 3D NAND technology) and by expanding the SSD business.   There are three parts to this Continue reading

Is an HDD/SSD Price Crossover Coming Soon?

Western Digital's 10TB Ultrastar He HDDThe SSD Guy was recently asked whether HDDs would continue, at least through 2019, to remain preferable to SSDs as cost-effective high-capacity storage.  The answer was “Yes”.

Longtime readers will note that I steadfastly maintain that HDD and SSD gigabyte prices are unlikely to cross for a very long time.  Historically, a gigabyte of NAND flash has cost between ten to twenty times as much as a gigabyte of HDD.  Let’s look at where Objective Analysis expects things to go by 2019.

Our current projections call for NAND price per gigabyte to reach 4.4 cents in 2019.  I would expect for HDD to still be 1/10th to 1/20th of that price.  Most likely 1/10th, since we expect for NAND flash to be in a significant oversupply at that time and will be selling at cost.

If HDD prices continue to hover around $50, then a 2019 HDD price of 0.44 to 0.22 cents per gigabyte (1/10th to 1/20th of the price of NAND flash) would imply an average HDD capacity of 11-23TB.

A couple of weeks ago, on December 2, 2015, Western Digital’s HGST introduced its Continue reading

Comparing DWPD to TBW

TBW-DWPDA couple of specifications for SSD endurance are in common use today: Terabytes Written (TBW) and Drive Writes Per Day (DWPD).  Both are different ways to express the same thing.  It seems that one vendor will specify endurance using TBW, while another will specify DWPD.  How do you compare the two?

First, some definitions.  “Terabytes Written” is the total amount of data that can be written into an SSD before it is likely to fail.  “Drive Writes Per Day” tells how many times you can overwrite the entire capacity of the SSD every single day of its usable life without failure during the warranty period.  Since both of these are guaranteed specifications, then your drive is most likely to last a lot longer than the number given by the SSD’s maker.

To convert between the two you must know the disk’s capacity and the warranty period.  If  drive maker gives you TBW but you want to know DWPD you would approach it Continue reading

SanDisk: SSD at HDD Prices

SSD & HDD Price vs CapacityYesterday SanDisk announced a new low-end family of SSDs that the company said would sell: “at a price point on par with HDDs. (Pricing comparison dependent upon capacity.)”  The sub-headline states: “Z400s SSD Brings New Levels of Affordability to Replace Hard Drives…”

The release provided no actual prices to back up this claim.

So how does this work?  Can you actually now buy a 1TB SSD for cheaper than a 1TB HDD?  Not at all.  Instead you have to look at things a little differently using a concept that I frequently explained five years ago when SSDs were pretty new – that very low capacity SSDs can be cheaper than HDDs.

This post’s graph plots this out.  It’s a chart of HDD and SSD prices over a range of capacities.  It’s on a log-log scale, but it works well on a standard linear chart as well.  Note that prices are for 2010, and prices have come down significantly for both SSDs and HDDs since then.  This means that the numbers on the X and Y axes need adjustment to bring them to today’s levels, but the shape of the curves would remain the same.

The red line represents SSD costs over the range of capacities, and the black line represents HDDs.  Although HDDs are cheaper than SSDs  Continue reading

MLC vs. eMLC – What’s the Difference?

eMLCFrom time to time IT managers ask The SSD Guy if there’s an easy way to compare SSDs made with MLC flash against those made using eMLC flash.  Most folks understand that eMLC flash is a less costly alternative to SLC flash, both of which provide longer wear than standard MLC flash, but not everyone realizes that eMLC’s superior endurance comes at the cost of slower write speed.  By writing to the flash more gently the technology can be made to last considerably longer.

So how do you compare the two?  OCZ introduced MLC and eMLC versions of the same SSD this week, and this provides a beautiful opportunity to explore the difference.

As you would expect, the read parameters are all identical.  This stands to reason, since Continue reading