Taking an Accurate Look at SSD Write Endurance
Last year, I posted a rebuttal to a paper describing the future of flash memory as ‘bleak’. The paper went through great (and convoluted) lengths to paint a tragic picture of flash memory endurance moving forward. Yesterday a newer paper hit Slashdot – this one doing just the opposite, and going as far as to assume production flash memory handling up to 1 Million erase cycles. You’d think that since I’m constantly pushing flash memory as a viable, reliable, and super-fast successor to Hard Disks (aka 'Spinning Rust'), that I’d just sit back on this one and let it fly. After all, it helps make my argument! Well, I can’t, because if there are errors published on a topic so important to me, it’s in the interest of journalistic integrity that I must now post an equal and opposite rebuttal to this one – even if it works against my case.
First I’m going to invite you to read through the paper in question. After doing so, I’m now going to pick it apart. Unfortunately I’m crunched for time today, so I’m going to reduce my dissertation into the form of some simple bulleted points:
- Max data write speed did not take into account 8/10 encoding, meaning 6Gb/sec = 600MB/sec, not 750MB/sec.
- The flash *page* size (8KB) and block sizes (2MB) chosen more closely resemble that of MLC parts (not SLC – see below for why this is important).
- The paper makes no reference to Write Amplification.
Perhaps the most glaring and significant is that all of the formulas, while correct, fail to consider the most important factor when dealing with flash memory writes – Write Amplification.
Before geting into it, I'll reference the excellent graphic that Anand put in his SSD Relapse piece:
SSD controllers combine smaller writes into larger ones in an attempt to speed up the effective write speed. This falls flat once all flash blocks have been written to at least once. From that point forward, the SSD must play musical chairs with the data on each and every small write. In a bad case, a single 4KB write turns into a 2MB write. For that example, Write Amplification would be a factor of 500, meaning the flash memory is cycled at 500x the rate calculated in the paper. Sure that’s an extreme example, but the point is that without referencing amplification at all, it is assumed to be a factor of 1, which would only be the case if you were only writing 2MB blocks of data to the SSD. This is almost never the case, regardless of Operating System.
After posters on Slashdot called out the author on his assumptions of rated P/E cycles, he went back and added two links to justify his figures. The problem is that the first links to a 2005 data sheet for 90nm SLC flash. Samsung’s 90nm flash was 1Gb per die (128MB). The packages were available with up to 4 dies each, and scaling up to a typical 16-chip SSD, that only gives you an 8GB SSD. Not very practical. That’s not to say 100k is an inaccurate figure for SLC endurance. It’s just a really bad reference to use is all. Here's a better one from the Flash Memory Summit a couple of years back:
The second link was a 2008 PR blast from Micron, based on their proposed pushing of the 34nm process to its limits. “One Million Write Cycles” was nothing more than a tag line for an achievement accomplished in a lab under ideal conditions. That figure was never reached in anything you could actually buy in a SATA SSD. A better reference would be from that same presentation at the Summit:
This shows larger process nodes hitting even beyond 1 million cycles (given sufficient additional error bits used for error correction), but remember it has to be something that is available and in a usable capacity to be practical for real world use, and that’s just not the case for the flash in the above chart.
At the end of the day, manufacturers must balance cost, capacity, and longevity. This forces a push towards smaller processes (for more capacity per cost), with the limit being how much endurance they are willing to give up in the process. In the end they choose based on what the customer needs. Enterprise use leans towards SLC or eMLC, as they are willing to spend more for the gain in endurance. Typical PC users get standard MLC and now even TLC, which are *good enough* for that application. It's worth noting that most SSD failures are not due to burning out all of the available flash P/E cycles. The vast majority are due to infant mortality failures of the controller or even due to buggy firmware. I've never written enough to any single consumer SSD (in normal operation) to wear out all of the flash. The closest I've come to a flash-related failure was when I had an ioDrive fail during testing by excessive heat causing a solder pad to lift on one of the flash chips.
All of this said, I’d love to see a revisit to the author’s well-structured paper – only based on the corrected assumptions I’ve outlined above. *That* is the type of paper I would reference when attempting to make *accurate* arguments for SSD endurance.
Subject: Storage | February 15, 2013 - 04:26 PM | Jeremy Hellstrom
Tagged: vector, ssd, sata, ocz, mlc, Indilinx Barefoot
Just in case you forgot how impressive the OCZ Vector 256GB is, Overclockers Club would like to remind you. The Indilinx Barefoot 3 controller is matched with low cost 25nm MLC IMFT NAND modules and 512MB of DDR3-1600 RAM for a cache. That translates to incredibly fast performance but without the high price of other drives. The 256GB model sits currently just under $1/GB, it is not the least expensive SSD available but when you consider the speeds this drive operates at it is the best value. Remind yourself where OCZ's Vector sits in the pack by reading on at OCC.
"OCZ's Vector line of solid state drives is every bit the performer that the Vertex 4 drives are with very few exceptions. In many of the tests, the two fastest drives were the Vertex 4 and OCZ's latest Indilinx Barefoot 3-equipped Vector. The only real weakness I saw was that the Vector was less frugal with the CPU cycles than the other Indilinx equipped drives. OCZ's move to the Barefoot 3 controller is beginning to pay dividends as it uses the technologies it has available in-house after the Indilinx and PLX acquisitions. It's taken a while to go all-in but that time has come. As the first totally in-house designed controller from OCZ, it seems to have hit on a controller that does better at managing real world usage scenarios and handling both compressible and incompressible data streams.”
Here are some more Storage reviews from around the web:
- OCZ Vector 256GB Solid State Drive Review @ OCIA
- Micron P400m 200GB Enterprise SSD @ Tweaktown
- Samsung 840 Pro 256GB SSD @ Tweaktown
- Samsung 840 SSD Storage Endurance Testing - TLC to the End @ Tweaktown
- kingston HyperX 3K 120GB SSD Review @ XtremeComputing
- Intel DC S3700 800GB Enterprise SSD @ Tweaktown
- Intel 525 Series mSATA SSD Performance Roundup @ Legit Reviews
- Plextor M5M 128GB review: the mSATA version of the M5 Pro @ Hardware.info
- Plextor 128GB M5M mSATA @ Kitguru
- MyDigitalSSD BP4 120GB SSD Review - SATA 3 At an Amazing Price @ SSD Review
- Micron P400m @ AnandTech
- Intel 525 mSATA SSD Review – Every Capacity Tested @ HCW
- Intel SSD 335 vs. Intel SSD 330 Review: Inexpensive SSD Evolution @ X-bit Labs
- Western Digital Red Hard Disk Drives for Network Attached Storage @ X-bit Labs
- Seagate Enterprise Capacity 3.5 V.3 4TB SATA III HDD Review @ NikKTech
- HighPoint RocketStor 5322 Review @ OCC
- Kingston Wi-Drive MobileLite Wireless Card Reader Preview @ Legit Reviews
- Kingston DataTraveler HyperX Predator 512GB Flash Drive Review @ Techgage
- Kingston DataTraveler Ultimate G3 64GB USB 3.0 Flash Drive Review @ NikKTech
- SanDisk Extreme 64GB USB 3.0 Flash Drive @ Tweaktown
- Thecus N5550 @ Legion Hardware
- Thecus Top Tower N8850 review: a powerful eight-disk NAS device @ Hardware.info
- 24 two-bay NAS device group test @ Hardware.info
- Transcend StoreJet 25M3 1 TB External USB 3.0 HDD Review @ OCC
Introduction, Specifications and Packaging
With newer and faster SSDs coming to market, we should not forget those capable controllers of yesteryear. There are plenty of folks out there cranking out products based on controllers that were until very recently the king of the hill. Competition is great for the market, and newer product launches have driven down the cost of the older SandForce 2281 SATA 6Gb/sec controller. ADATA makes a product based on this controller, and it's high time we gave it a look:
The ADATA XPG SX900 launched mid last year, and was ADATA's first crack at the eXtended capacity variant of the SandForce firmware. This traded off some of the spare area in the interest of more capacity for the consumer.
Subject: General Tech | February 6, 2013 - 01:35 PM | Jeremy Hellstrom
Tagged: vector, ssd, ocz, giveaway, far cry 3
If you purchase a 256GB or 512GB OCZ Vector Series drive before July 14th of 2013 you will get a free downloadable copy of Far Cry 3, to a maximum of two copies. Allyn was more than impressed with this drive, finishing off his review with the statement that "The OCZ Vector astonished me with its throughput, sheer IOPS performance, and low latency", with the only negative comment involving the drives inability to do household chores. They are not the least expensive drives on the market but they are some of the fastest and they come with a 5 year warranty as well.
Subject: Storage | February 5, 2013 - 03:16 AM | Tim Verry
Tagged: ssd, SandForce SF-2281, sandforce, mlc, intel 335, Intel
Intel has added a new drive to its existing 335 SSD series. The new drive offers up 180GB of storage, but maintains the same level of read and write performance as its larger 240GB sibling.
The 180GB version uses 20nm MLC NAND flash paired with a SandForce SF-2281 controller. According to the Intel-provided spec sheet (PDF), the new drive is capable of sustained read and write speeds of 500 MB/s and 450 MB/s respectively. Further, the drive maxes out at 42,000 random read IOPS and 52,000 random write IOPS.
The drive will come in the 2.5” form factor, but is 9.5mm thick (meaning it will not work in all notebooks). Reportedly, Intel has redesigned the casing to include a schematic/blueprint graphic alongside the Intel logo.
Intel rates the 180GB 335 series SSD at 1.2 million MTBF and is warranted for three years. The drive can currently be found online for around $180, making it right around the $1/GB mark. Interestingly, the larger 240GB model is currently retailing for around $195. Therefore, if you can spare the extra $15, the 240GB model is the better deal.
Introduction, Specifications and Packaging
It has been just under a year since Intel released their 520 Series SSD, which was their second 6 Gb/sec SATA unit. Sporting a SandForce controller, that release helped bridge a high speed storage gap in their product lineup. One year prior, Intel dabbled in the mSATA form factor, releasing a 310 Series model under that moniker. The 310 showed up here and there, but never really caught on as the physical interface was admittedly before its time. While in hindsight it was a very good way to go towards establishing a fixed standard, the industry had already begun fragmenting on these smaller interfaces. The MacBook Air had already launched with a longer 'GumStick' shaped SSD, and Ultrabook makers were following suit with units that were physically identical yet not pin-compatible with that used in the Apple product.
The Intel 520 Series SSD helped push Intel into 6Gb/sec SATA territory.
It's taken a while for the industry to favor defragmentation (pun intended) enough for mSATA to really start catching on, and that time appears to be nearing with Intel's launch of the SSD 525 Series:
Subject: Storage | January 17, 2013 - 03:05 PM | Jeremy Hellstrom
Tagged: DC S3700, Intel, ssd, HET MLC, enterprise ssd
Before getting into the speed of the new Intel DC S3700 SSD, take a moment to consider the expected lifespan of the HET MLC flash, it was described to hardCOREware as "10 full drive writes per day over the 5-year life of the drive". Now that will not have a big impact on home users, but Enterprise and image/video editors will certainly take note as moving that much data is a common occurrence for those businesses and the questionable lifespan of some flash memory has been contributed to the slow pace at which SSDs have been taken up by large businesses. With the Intel name behind these drives, an assurance of long term usability and the impressive steady state performance they provide you may soon see these in a server room near you.
"The Intel SSD DC S3700 introduces a new Intel SSD controller for the first time in years. With a heavy emphasis on consistent performance, these drives bode well for the future of Intel SSD products. It may also refresh your opinion on some current SSDs that don't perform as consistently as others once they enter a steady state."
Here are some more Storage reviews from around the web:
- SanDisk Ultra Plus SSD @ SSD Review
- OCZ Vector 256GB SSD Review @ Techgage
- Kingston SSDNow V300 120GB SSD Upgrade Kit Review @ NikKTech
- OCZ Vector 512GB @ Legion Hardware
- Samsung 840 Pro 128GB SSD @ Tweaktown
- SanDisk Ultra Plus SSD @ AnandTech
- Micron P320h PCIe Enterprise SSD @ Tweaktown
- oshiba THNSNF 512GB SSD review: with proprietary controller @ Hardware.info
- Western Digital RE 4TB HDD @ TechwareLabs
- ICYDock MB981U3N-1SA SATA/IDE Hard Drive Adaptor @ PCSTATS
- Patriot Gauntlet (PCGTW320S) @ Bjorn3D
- EonNAS 1100 NAS Network Storage Server @ Benchmark Reviews
- Synology DS413j NAS Designed for Home & Offices Review@ Madshrimps
- ADATA DashDrive UD310 Jewel-Like Flash Drive Review @ Pro-Clockers
- Kingston DataTraveler HyperX Predator 512GB @ Kitguru
- Patriot SuperSonic Rage XT 32GB USB 3.0 Flash Drive Review @ NikKTech
- Kingston DataTraveler HyperX USB 3.0 64 GB @ techPowerUp
- Kingston DT Elite USB 3.0 64GB Thumb Drive Review @ XtremeComputing
- Kingston DataTraveler HyperX Predator 512GB USB 3.0 Flash Drive Review @ Legit Reviews
Subject: General Tech | January 16, 2013 - 03:58 PM | Jeremy Hellstrom
Tagged: ocz, price increase, price cuts, ssd
The hard drive market has recovered somewhat over 2012 from the sharp spike in prices we saw as a result of the flooding in Thailand, though never to the prices we became used to in 2011. That issue fell by the wayside in 2013 thanks to the sharp drop in prices for SSDs, with a price of $1/GB becoming a common price point even before specials and deals are considered. The Tech Report noticed something different about Q4 of 2012, with the pricing trend actually reversing and many drives increasing in price by 10-20%. In part this might be accounted for due to the drop in overall PC sales but The Tech Report has another culprit in mind, read on to see why you might have OCZ to thank for both the rapid drop in SSD prices as well as the current upwards trend.
"SSD prices fell by 38% in 2012. However, they actually went up in the fourth quarter, spurred largely by an end to OCZ's deep discounts. We've crunched the numbers for more than 40 drives to get a better sense of what's going on."
Here is some more Tech News from around the web:
- Android Programming: Multiple-Choice Lists @ Linux.com
- Symantec to offload Altiris: report @ The Register
- Latest Java patch is not enough, warns US gov: Axe plugins NOW @ The Register
- TEXT GOES HERE
- CES 2013 Coverage - Day 0: ASUS, Thermaltake, Enermax, beQuiet!, Lepa, MSI, NERO @ Hi Tech Legion
- CES 2013: Gigabyte Shows Off Thin Mini ITX Motherboards for Smart TVs @ Funky Kit
- Final Coverage of CES 2013 @ OCC
- Print your own 30 round AR15 magazine @ Hack a Day
Subject: Storage | January 7, 2013 - 06:57 PM | Jeremy Hellstrom
Tagged: ssd, sandisk ultra plus, 256GB, Marvell, 88SS9175
Using the Marvell 88SS9175 controller, the SanDisk Ultra Plus family of SSDs comes in 128GB, 256GB and 512GB models all of which come with a 3 year warranty. As you can see below, the 256GB model that Legit Reviews recently received does not take up much space in the drives shell. SanDisk's nCache technology is featured on these drives and helps boost the performance of 4k writes but does not fare so well on large files. With decent performance and a price under $1/GB these drives are worth checking out ... unless you want to wait to see what comes out of CES.
"SanDisk is best known for their memory products and with that, they've been doing a number of SSDs on both consumer and enterprise fronts. Their latest offering that came across our desk is the Ultra Plus line being powered by the Marvell 88SS9175 controller and SanDisk's own 19nm NAND. The 6Gbps interfaced drives are marketed towards the both the desktop and mobile computing crowds with promises of strong performance, high reliability and power efficiency. It comes standard in the 7mm, 2.5" form factor so it should be good to go for most Ultrabooks as well..."
Here are some more Storage reviews from around the web:
- SanDisk Ultra Plus SSD @ AnandTech
- KingFast F3 Series 2.5" SATAIII SSD 240GB KF2509MCF Review @ Madshrimps
- Understanding MTBF in SSD - What Does an SSD's MTBF Mean for You @ hardCOREware
- Mushkin Chronos DX 480GB @ Tweaktown
- Kingston SSDNow KC100 240GB SSD Upgrade Kit Review @ NikKTech
- Rosewill RDED-12001 External Slim Aluminum Blu-Ray Writer @ Hi Tech Legion
- LaCie 5big NAS Pro @ AnandTech
- Asustor AS-606T NAS @ techPowerUp
- Infortrend EonNAS Pro 200 2-Bay NAS @ Tweaktown
- LaCie 5big NAS Pro Preview: User-friendly hybrid cloud @ Hardware.info
Subject: Storage | January 7, 2013 - 09:55 AM | Tim Verry
Tagged: x110 ssd, ultra plus, ssd, sandisk, ces 2013, CES, 19nm
SanDisk has officially launched a new solid state drive that is slated to offer up a good balance of performance and price. Based on 19nm flash used in a 2.5” form factor drive acceptable for either notebook or desktop upgrades, the new drive is the Ultra Plus in retail channels and known as the X110 to OEM partners.
The basic specifications that SanDisk have released include a SATA 3.0 6Gbps connection, and respectable sequential read and write speeds of 530 MB/s and 445 MB/s respectively. Random read and write speeds and IOPS were not listed in the press release.
However, in an odd twist for CES news, the new SanDisk solid state drive is actually available now at Amazon, Microcenter, and Newegg. Amazom and Microcenter will have 64GB, 128GB, and 256GB SKUs while Newegg will carry the 128GB and 256GB models.
Interestingly, SanDisk has priced these drives fairly cheaply with MSRPs of $79.99 for the 64GB model, $109.99 for the 128GB model, and $219.99 for 256GB drive. Granted the 64GB model is not great on $/GB, but the higher tier models are under $1/GB. Unfortunately, the 128GB model is out of stock on Amazon, and the 64GB and 256GB models are all well above MSRP at $120 and $250 respectively. Here’s hoping the price comes down as more stock becomes available.
PC Perspective's CES 2013 coverage is sponsored by AMD.
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