SandForce SF-2141: The Odd Kid in Class
In our article that covered SandForce's SF-2000 Series Client announcement, we found a pair of controllers that were a little out of place; these being the two SF-2100 Series drives, SF-2141 and SF-2181, the SATA 3G products that no one has really talked about. The 2100 Series at first appear to be low cost drives, possibly developed for the mSATA market. Even though they have similar specifications, they are very much unique in capability.
Let's focus on the SF-2141 since it's directly related to this editorial. The SF-2141 is a 4-channel, 4 byte lane SATA 3G controller with a 14mm square die package size. The flag that pops up when we start connecting the dots is that the SF-2141 has a maximum capacity size of just 64GB. We've seen 4 channel SSDs before, the main one that comes to mind is the Indilinx Barefoot. The Barefoot was offered in capacity sizes of up to 256GB.
The rest of the SF-2141 specifications look like this. 250MB/s read and write speed, 60K 4k IOPS read, 60K 4k IOPS write burst, 10K 4k IOPS sustained.
The next dot has to do with the use of SLC flash with the 2000 Series Client family. Aside from the SF-2141, every other 2000 Series controller is restricted to a significant capacity decrease when SLC flash is used. Even the SF-2282 with 8 channels, 16 byte lanes that is capable of delivering up to 512GB of MLC flash is restricted to just 128GB of SLC. Our suspect SF-2141 can use 64GB of MLC or SLC, no restrictions for high speed, long endurance SLC flash.
I think this is going to be a very important issue when we start actually using the Z68 chipset that is limited to just 64GB of flash use. I've never been a fan of small SSDs, especially small SSDs using MLC flash that is guaranteed to wear out much faster than larger capacity drives.
In our SandForce SF-2000 Client Series article I also talked about the options SandForce opened for drive manufacturers. Several flash types being supported received most of the attention, but we didn't let 'Binary User Capacity Points (RAISE Off Mode) slip by without a mention. At the time my speculation was that we'd see SF-2200 drives hit the market without RAISE and have capacities of 128GB and 256GB as opposed to 120GB and 240GB, the standard for SandForce consumer drives. This still might be the case - please send samples my way for testing and I'll let you know how that goes :)
Now I'm more inclined to think the ability for manufacturers to enable or disable RAISE has more to do with the Intel Smart Response Technology than our standard Team SandForce 2.5" drives that we all love.
There are three options available; Off, Enhanced (Default) and Maximized. Enhanced uses write-through data caching and Maximized uses write-back data caching. VR-Zone describes the two modes as such:
Enhanced mode is the default acceleration mode as it offers data protection in the case of disk failure. It uses write-through data caching method to write data to the SSD and hard drive simultaneously. For user who wants maximum disk performance, you can choose the maximized mode but there is a high risk of data loss during disk failure. It uses the write-back cache method where data is written from the Cache SSD to the disk at intervals. For even better disk performance, you can first stripe your hard drives then choose maximized mode. User can change acceleration mode at any time as long as the SSD and hard drive are working normally.
The Enhanced (Default) mode appears to be primarily a read mode for the SSD. Obviously writes have to occur at some point, but not to the same degree as the Maximized setting. On VR-Zones chart at the bottom of the page Enhanced has a performance listing as Run-Time Read, but in the same performance column the Maximized option says Run-Time Read and Run-Time Write. I think this is going to really open the door for SSD manufacturers to justify both MLC (for Enhanced use) and SLC (for Maximum use) scenarios.
One option I'd liked to see opened up for the Maximum setting drives if they are made is carried over from SandForce's enterprise product line up. SandForce has a unique way of handling power failures on enterprise specific models. By using a capacitor called a SuperCap, data can be written to the flash after a power interruption has occurred. On our chart at the top of this page under the category of Power Failure Circuit Support for the SF-2141, it says that it is not a supported option. Let's cross our fingers and hope someone has a change of heart on that one.