SSD Interfaces

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

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

OCZ Comes Roaring Back with NVMe SSD Debut

The OCZ Z-Drive 6000It’s really something to see a company recover from a big challenge, and signs of that happened this week with OCZ’s introduction of a new NVMe-based PCIe SSD they call the Z-Drive 6000 series.

This replacement for the company’s Z-Drive 4000 series is a complete redesign with an obsession for performance.  OCZ tells me that they moved from a 2-hop design to a 1-hop by using the PMC Princeton PCIe SSD controller, and have passed the University of New Hampshire Interoperability Labs’ compliance tests to NVMe 1.1B compliance.

But how does it perform?  Well the 1-hop design helps reduce latency (which is just starting to overshadow IOPS in users’ minds) and the latency of this SSD is significantly lower than competing NVMe SSDs: between 25-30μs, figures that OCZ tells me are very consistent, a big plus for enterprise applications.  As for IOPS, the device can perform under a 70/30 Read/Write load at 330K.

The 6000 series is provided in both standard MLC and eMLC for those who want the security of eMLC and are willing to sacrifice a little performance to sleep better at night.

This product is a good fit for the market needs, and shows how devoted OCZ and its parent Toshiba are to providing high performance in the SSD marketplace.

 

Where does NVRAM Fit?

AGIGARAM DDR4 NVDIMM (Photo Courtesy of AgigA Tech)There’s been a lot of interest in NVRAM recently.  This technology has been lurking in the background for decades, and suddenly has become very popular.

What is NVRAM?  Quite simply, it’s DRAM or SRAM that has a back-up flash memory a small controller, and a battery or super-capacitor.  During operation the DRAM or SRAM is used in a system the same way that any DRAM or SRAM would be used.  When power is interrupted the controller moves all of the data from the DRAM or SRAM to the flash using the backup power from the battery or super-capacitor.  When power is restored, the controller moves the contents of the flash back into the SRAM or DRAM and the processor can resume operation where it left off.

In some ways it’s storage and in some ways it’s memory, so Continue reading

White Paper: Matching Flash to the Processor

Moving flash into the memory channel to get fast parallel performance I have just added a new white paper onto the Objective Analysis website: Matching Flash to the Processor – Why Multithreading Needs Parallelized Flash.

This document examines the evolution of today’s CPUs, whose clock frequencies have stopped increasing, but now exploit parallelism to scale performance.  Multiple DRAM channels have also been added to performance computing to add parallelism to the memory channel.

Storage hasn’t kept pace with this move to parallelism and that is limiting today’s systems.

New NAND flash DIMMs recently introduced by Diablo, SanDisk, and IBM, provide a reasonable approach to adding parallel flash to a system on the its fastest bus – the memory channel.  This white paper shows that storage can be scaled to match the processor’s growing performance by adding flash DIMMs to each of the many DRAM buses in a performance server.

The white paper is downloadable for free from the Objective Analysis home page.  Have a look.

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

Diablo: Flash Belongs on the Bus

Diablo TechnologiesDiablo Technology has just introduced a new set of DIMMs that put flash memory right onto the DDR3 memory bus.

I can already hear readers saying: “Wait!  You can’t do that!”  Well, you’re right, but the new module comes awfully close to that by putting the NAND behind an ASIC that interfaces between the DDR3 bus and the NAND.

Why do this?  Quite simply because you can get more “Bang for the Buck” by adding NAND to the system once you’ve reached a certain DRAM size.  The Diablo “Memory Channel Storage” (MCS) approach supports the addition of terabytes of NAND at the loss of Continue reading

WDC’s HGST Intros 12G SAS MLC SSDs

Latencey Histogram of HGST's MLC SSDIn case you didn’t have enough abbreviations in your life, The SSD Guy brings you the headline above, with the promise that the news below is really interesting: HGST (formerly Hitachi Global Storage Technology, but now a division of WDC – Western Digital Corp.) has brought out a new line of 12Gb/s SAS SSDs based on MLC flash.  These are a part of the UltraStar line.

Whereas HGST’s first-generation UltraStar SAS SSDs used SLC flash, the new SSDs are based on 25nm MLC flash but offer the same warranties as HGST’s prior generation.  Even so, performance for the new SSDs is significantly faster than that of their SLC-based predecessors, with no reduction in wear or lifetime specifications.

These SSDs are the first to support Continue reading

One-Hop vs. Two-Hop PCIe SSDs

Bunny HopLately a number of PCIe offerings have hit the SSD market.  The SSD Guy breaks them into two camps: One-Hop SSDs, in which the commands are translated directly from PCIe to the NAND flash without going through an intermediary protocol, and Two-Hop SSDs, which use off-the-shelf HBAs and SATA SSD controllers to move commands first from PCIe to SATA then from SATA to NAND.  There are aslo versions that go through SAS: PCIe to SAS, then SAS to NAND.

The SSD Guy figured that Easter would be a good time to talk about these since everyone already has the Easter Bunny hopping through their minds!

It’s not hard to understand why Continue reading

Intel Intros Fast Datacenter SATA SSD

IOPS Over Time - Competing SSD vs. Intel DC S3700Today Intel announced a new SATA III SSD, the DC S3700 Series.  The new product is fast, supporting 75,000 random 4K read IOPS and 36,000 random 4K write IOPS.  Average read latency is 45microseconds (µs) with writes averaging 65µs.  Sustained sequential reads are 500 megabytes/sec with sustained sequential writes at 460.  The read performance of this SSD, although a SATA device, is twice that of Intel’s 710 PCIe SSD announced in April, and writes are a full 15 times faster.  Intel calls this performance: “Scary fast!”

Intel says this device is its best Continue reading