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Raw Bit Error Rate in SSD's with Shrinking Manufacturing Processes
The new SSDs based on new process technologies are getting more cost-effective and affordable, and the performances are also increasing as the new controllers are developed.
When talking about SSDs, maximum performances are the main focus of interest.
Let's take a look at the reliability of the stored data here.
The bit error rate (BER) is the number of bit errors divided by the total number of bits transferred. The data transfer error is usually corrected with ECC in computing, and thus keeping the data more safe and accurate.
The raw bit error rate (RBER) is the number of bit errors without ECC checksum divided by the total number of bits transferred.
The RBER is useful when evaluating the reliability of the data transferred from a storage device. The consumer semiconductor products are manufactured with more shrinking process design rules for pursuing low-cost. But as the design rules shrink, the RBER increases because the amount of electrons in the floating gate gets less. This could be a touchy issue which the manufactures may not want to open up, so I have tried to measure some of them.
Specifications of the test system are:
On November 28th, 2010, I have measured raw bit error rates of 43nm NAND flash from Toshiba and 34nm NAND flash from IM Flash Technologies (IMFT).
S.M.A.R.T. logs for Indilinx controllers are precisely described in the Transcend data sheet, using this information, Lansen wrote a program "JSMonitor v0.4c" (download). In the table in this program, "total error bits count" and "total sectors read" are obviously shown in green lines as in this site (http://d.hatena.ne.jp/Lansen/20101020/1287590139). You can use other S.M.A.R.T. information reading tools like CrystalDiskInfo, but JSMonitor v0.4c is more suitable for this experiment purpose for people like me, because numerical value in CrystalDiskInfo is displayed by hexadecimal number system and that in JSMonitor decimal system.
SuperTalent FTM64G225H was chosen for the SSD with 43nm Toshiba NAND flash, and OCZ OCZSSD2-1ONYX32G was chosen for the SSD with 34nm IMFT NAND flash, both of which are driven by Indilinx controllers (Barefoot and Amigos).
Toshiba IMFT
One of the 4,194,304KB Acronis backup files was picked up and the file was written into each SSD seven times, total of which is 28GB. OCZ SSD is filled with data mostly and SuperTalent SSD is filled halfway as in these property screen shots below.
Toshiba IMFT
Testing SSD and a 1TB Seagate HDD are placed at the SATA ports of the test system. The 28GB data files are copied from the SSD to the HDD and the RBER is calculated as in this article.
Raw bit error rate (RBER) = (Total error bits count) / (Total sectors read x 4,096)
The value of "total sectors read" is multiplied by 4,096 to obtain the value of "total bits read". This measurement is repeated four times until total of 112GB data file read-out is made from the SSD. Every time after the 28GB read-out is made, the RBER is calculated to see if the measurement test is going on a steady pace and the results are shown below. The SuperTalent SSD is a completely new one from the box, and the initial state of the OCZ SSD is a little different from new one because it was benchmarked a little before this test.
RBER MEASUREMENTS 1
Fig.1a Toshiba Fig.1b IMFT
RBER = 4,508 / (58,840,774x4096) = 1.87E-8 for SuperTalent FTM64G225H with Toshiba NAND.
RBER = 171,937 / (66,904,795x4096) = 6.27E-7 for OCZ OCZSSD2-1ONYX32G with IMFT NAND.
RBER MEASUREMENTS 2
Fig.2a Toshiba Fig.2b IMFT
RBER = 8,929 / (117,561,671x4096) = 1.85E-8 for SuperTalent FTM64G225H with Toshiba NAND.
RBER = 335,037 / (125,626,716x4096) = 6.51E-7 for OCZ OCZSSD2-1ONYX32G with IMFT NAND.
RBER MEASUREMENTS 3
Fig.3a Toshiba Fig.3b IMFT
RBER = 13,320 / (176,324,533x4096) = 1.84E-8 for SuperTalent FTM64G225H with Toshiba NAND.
RBER = 495,977 / (184,348,125x4096) = 6.57E-7 for OCZ OCZSSD2-1ONYX32G with IMFT NAND.
RBER MEASUREMENTS 4
Fig.4a Toshiba Fig.4b IMFT
RBER = 17,704 / (235,045,302x4096) = 1.83E-8 for SuperTalent FTM64G225H with Toshiba NAND.
RBER = 656,167 / (243,070,046x4096) = 6.59E-7 for OCZ OCZSSD2-1ONYX32G with IMFT NAND.
RBER MEASUREMENTS 5b
On this site (http://d.hatena.ne.jp/Lansen/20101119/1290188657), Lansen is making an experiment to see the data retention ability or data losing risk of the SSDs with worn-out NAND flash memory cells. His initial test for preparation is mostly identical with mine.
His initial results are:
RBER = 1.81E-8 for SuperTalent FTM64G225H with Toshiba NAND.
RBER = 1.83E-7 for OCZ OCZSSD2-1ONYX32G with IMFT NAND.
The result with Toshiba NAND is identical with mine, but the RBER test result with IMFT NAND is almost one third compared with my test result. For getting statistical results as in a research project, the more numbers of SSDs we study, the more accurate the statistical results are. As a consumer, all I could do was to examine another one.
This time, the testing method is identical with the first one above except that the data receiving device is ANS-9010.
Fig.5b IMFT
Final result for the second one:
RBER = 443,069 / (243,675,221x4096) = 4.47E-7 for OCZ OCZSSD2-1ONYX32G with IMFT NAND.
The result of the second measurement is closer to his result but three data seems to vary. I had imagined that this could be attributed to the difference of the site, like central or peripheral, where the die is taken from the large silicon wafer.
(All NAND flash devices are NOT created eqaul! Reason.)
RBER MEASUREMENTS 5a1 and 5a2
I then started to think that I need to measure another SSD with Toshiba NAND flash.
As in the case with Toshiba NAND flash, the RBER in the data transfer like the one I did above and the RBER during benchmarks are different, the latter is evidently higher.
The second SuperTalent FTM64G225H is already abused with benchmarks, so for the second test for the Toshiba NAND flash, I had decided to calculate RBER during the data transfer by using the difference of the two values.
Fig.5a1 Toshiba Fig.5a2 Toshiba
RBER = (28,711-12,809) / {(277,408,506-34,490,665)x4096} = 1.60E-8 for SuperTalent FTM64G225H with Toshiba NAND.
Here is the table of the results including Lansen's and mine:
***************** Raw Bit Error Rate in SSDs **************** | ||
Toshiba NAND | IMFT NAND | |
SSD No.1 | 1.83E-8 | 6.59E-7 |
SSD No.2 | 1.60E-8 | 4.47E-7 |
Lansen's SSD | 1.81E-8 | 1.83E-7 |
AVERAGE | 1.75E-8 | 4.30E-7 |