New Flash Performance - Page 3
While Samsung is the first out of the gate with 3D NAND chips, they definitely won't be the only one. The Intel-Micron joint effort announced that in the second half of 2015 they will have a 256 Gbit (32GB) capacity die that uses 32 layers (MLC) [Note: Samsung is currently using a 120 Gbit die]. They will also have a 384 Gbit (48GB) die that uses TLC, increasing the flash chip density by 50 percent.
Recently, Toshiba announced a 48-layer 128Gbit (16GB) 3D NAND chip. They are sampling these chips now, but the speculation is that they will ship a drive in 2016.
The advent of 3D NAND chips has just started to impact the flash drive market, but it is expected to have a significant impact in the coming two to three years. If you couple this with TLC chips, then you can see the flash chip density is likely to increase quickly with the result that the flash drive prices should decrease.
As vendors started to develop flash drives they soon realized that drives were throttled by the current storage buses, SATA and SAS. In addition to dropping the price of flash chips, vendors started looking for ways to improve performance by going around SATA and SAS.
Ever since Fusion-io introduced SSDs that attached using the PCIe bus, people have realized that the SATA and SAS buses are definitely inhibiting performance. On the one hand, SATA and SAS buses allow drives to be easily connected and used as IO devices. All of the existing software infrastructure could be used with these buses. On the other hand, using them holds back performance. Therefore, vendors have started to examine using the PCIe bus to really take advantage of the performance of these drives.
In addition to the PCIe bus, the new SATA Express interface offers improved performance options for consumer drives. It supports both SATA and PCIe storage devices. In particular, the M.2 specification for internally mounted expansion cards offers the option of physically small SSD devices with good performance.
As mentioned previously, PCIe flash drives have been around for a while, starting with Fusion-IO. The current prices have been a little high and vary by a fair amount. As of 4/5/2015, consumer PCIe drives started around $0.67/GB and went to $5.00/GB with a typical price range of $1.00/GB to $3.00/GB. These are 2x to almost 20x the price of SATA or SAS drives, but the trade-off is that you get much greater performance. For example, for a high-end drive, you can get up to 2.8 GB/s for reads and writes, and about 410,000 random IOPS for reads and writes. The typical performance is a bit less than this, but it illustrates what kind of performance PCIe offers.
The early PCIe SSD drives all had their own drivers, which made life a little difficult. The recent NVMe(Non-Volatile Memory Express) specification was developed to standardize on a logical device interface so operating systems only need one driver. Most importantly, the specification takes into account the low-latency nature of PCIe SSDs and the parallelism of current CPUs and PCIe SSDs. The interface applies to both PCIe devices and SATAe/M.2 devices.
There have been NVMe drives for a bit, but an example of a recent drive is the Intel SSD 750. It's not quite available as of the time of this writing, but the preliminary performance is quite good. The smaller drive, 400GB, can reach 2.2 GB/s reads, 900 MB/s writes, 430K random read IOPS, and 230K random write IOPS. The price for the smaller driver and the larger 1.2TB drive are both about $1.00/GB. This illustrate the extreme performance from NVMe drives and the rapidly decreasing prices.
M.2 drives are also becoming quite prevalent. They are physically very small, but then again, flash chips are small. Despite this, they currently range in size up to 1TB. For example, Samsung has the 840 EVO mSATA drive that uses TLC chips. Also, recently, they have introduced a 3D NAND M.2 drive, the M.2 850 EVO that uses TLC as well. Both drives are capable of about 520-540 MB/s for reads and writes and about 88-95K of random IOPS (read and write).
For a period of time, it didn't look like flash drives were going to decrease in price very much. Flash cell technology is limited to around 20nm because of cost and complexity considerations, but manufacturers have found ways around the limitation. Rather than decrease the features size, they now store more bits per cell (TLC) and have started to create 3D flash chips. This combination, plus the growth in flash storage sales, has driven down the price per gigabyte.
Flash drive vendors aren't totally focused on price though. They have also been working on ways to take advantage of the flash drives by utilizing other system buses, specifically the PCIe bus. The somewhat new NVMe specification has standardized PCIe storage devices, reducing the burden on writing drivers and adding more headroom on performance via parallelization. When flash storage is put in the PCIe bus, you can see amazing performance from single drives.
These next couple of years with flash drives are going to be exciting.
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