SSD Reliabiity

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

Extreme ECC Enables Big SSD Advances

Combined University Seals Trzetrzelewska Univerity & UN-NeWA new and highly-efficient error correction scheme has recently been revealed by a joint university research team.  The SSD Guy has learned that this largely-overlooked research, performed by a cross-university team from University of North by Northeast Wales in the UK (UN-NeW) and Poland’s Trzetrzelewska University, could bring great economies to SSD manufacturers and all-flash array (AFA) companies.

Dr. Peter Llanfairpullguryngyllgogeryohuryrndrodullllantysiliogogogoch of UN-NeW, who generally shortens his name to Llanfairpullguryngyll and Dr. Agnieszka Włotrzewiszczykowycki of Trzetrzelewska University have determined that today’s more standard ECC engines can be dramatically improved upon to both increase available storage for a given price while accelerating throughput.  This is achieved through the use of new and highly complex algorithms that differ radically from current ECC approaches that are simply linear improvements upon past algorithms.

According to Dr. Włotrzewiszczykowycki: “The beauty of semiconductors is that Moore’s Law not only allows Continue reading

IBM Upgrades DS8000 Series: All Models are now All-Flash

IBM DS8000 FamilyOn January 12 IBM announced some very serious upgrades to its DS8000 series of storage arrays.  Until this announcement only the top-of-the-line model, the IBM System Storage DS8888, was all-flash while the less expensive DS8886 and DS8884 sported a hybrid flash + HDD approach.  The new models of the DS8886 and DS8884 are now also all-flash.

But that’s not all: Every model in this product family has been upgraded.

The original DS8000 systems used a module called the High Performance Flash Enclosure (HPFE) for any flash they included, while these newer models are all based on HPFE Gen 2.  While the original HPFE was limited to a maximum capacity of 24TB in a 1U space, the larger 4U HPFE Gen 2 can be configured with as much as 153.6 TB, for more than six times the storage of the previous generation.  By making this change, and by optimizing the data path, the Gen 2 nearly doubles read IOPS to 500K and more than triples read bandwidth to 14GB/s.  Write IOPS in the Gen 2 have been increased 50% to 300K, while write bandwidth has been increased by nearly 4x to 10.5GB/s .

This kind of performance opens new Continue reading

Micron Unveils New 5100 Enterprise SSDs

Micron's 5100 SSD FamilyMicron has announced a new line of Enterprise SSDs that it has named the 5100 family.  The three members of the family are designated by different suffixes: 5100 ECO, 5100 PRO, and 5100 MAX, as listed in the table below.

The three models support the same maximum read IOPS performance, but have a wide range of write IOPS figures, endurance (measured in DWPD = Drive Writes per Day), and maximum capacities.

All of these SSDs are based on Micron’s 3-bit 3D NAND.  Micron has been aggressively ramping its 3D NAND technology since it began shipments in earnest last June.

The three SSD models are designed using the same fundamental firmware architecture, which Micron has named FlexPro, to yield consistent performance and reliability across the family, and with the hopes that customers will be able to qualify all three models in a single effort, which would provide one more reason for users to source their 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

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

What’s In My SSD? SLC, MLC, or TLC?

SLC, MLC, or TLC?Someone recently asked The SSD Guy if there is a way to determine whether an SSD is SLC, MLC, eMLC or TLC.

I found it a little odd to be asked this, since most vendors tell what kind of flash they use in an SSD’s specifications, especially if it’s SLC.

Not finding it there then the next thing I would look at is the price.  Raw SLC NAND flash now sells for about 6-10 times as much as its MLC counterpart, so an SSD with a price of around $1/GB is likely to be MLC and one that sells for around $10/GB is probably SLC.

TLC SSDs are really rare.  There is the Continue reading

LSI SandForce SSD Controllers Move the Knee in the Curve

LSI SandForce SF3700 Controller DuraWrite ImprovementsLSI’s SandForce has just rolled out its SF3700 family of four SSD controllers aimed at the Entry Client, Mainstream Client, Value Enterprise, and Enterprise Storage marketplaces. Performance is impressive, with worst-case random PCIe IOPS at 150K read/81K write and 94K/46K for the SATA interface.

The SF3700 family builds on the division’s first two product families by adding a choice of PCIe or SATA interfaces, LDPC error correction, and a boosted set of flash management features.  The SSD Guy will explore this last point after highlighting the other two.

By providing both PCIe and SATA interfaces LSI is directly addressing the future: PCs are aiming to move to the m.2 SSD specification rather than Continue reading

Solving SSD Power Spike Issues

The following guest post was contributed by Doug Dumitru the CTO of Easy Computing Company (EasyCo), a software R&D company which develops and markets SSD performance enhancement solutions

Doug Dumitru, EasyCoIt would appear that you could build an all-SSD array by simply replacing all of the HDDs in a cabinet with SSDs.  I tried that and ran into some surprising issues that were very confusing at first.

SSD spec sheets, might lead you to believe that power is just not an issue.  For example, Samsung lists the power use for a 512GB 830 SSD at 0.127W (typical) for “Active Power Use”.  This implies very low demands on the system power supply.

If you do some more research, you find that the peak power usage is a lot higher.  AnandTech, in a review article reports sequential write power draw at 5.14W and random write power draw at 5.8W. In that 2.5” SSDs use the 5V power rail exclusively, this is more than Continue reading

Webinar: Flash Best Practices

I had the opportunity to participate in a round table webinar covering the best practices for solid state storage on July 18.  The hour-long session (including Q&A) can be replayed at BrightTalk.

In this round table webinar entitled Best Practices for Solid State Storage Implementation storage analyst Tom Coughlin moderated three of us, Radoslav Danilak of Skyera, Esther Spanjer of SMART Storage Solutions, and The SSD Guy (Yours Truly) in a Continue reading