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How does a Sandforce controller work?

post #1 of 7
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So I've heard about Sandforce controllers compressing the data it receives to achieve higher write speeds, but how does that work? Does this mean the drive has more space because the controller compresses everything? So a 64GB drive can be a 128GB drive if all the data on the drive were compressible?
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post #2 of 7
I don't know if it compresses everything, but as far as I can surmise, a 64 GB drive has 64 GB of space.
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post #3 of 7
The sandforce controllers do compress data in order to achieve higher write speeds and slightly extend the life of the drive, however the compression will NOT add to the available space on the drive. It's a limitation in the way windows addresses drive space, the controller just uses the extra space for over-provisioning.
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post #4 of 7
Quote:
Originally Posted by TopGunSF View Post

The sandforce controllers do compress data in order to achieve higher write speeds and slightly extend the life of the drive, however the compression will NOT add to the available space on the drive. It's a limitation in the way windows addresses drive space, the controller just uses the extra space for over-provisioning.

Actually, I do believe the goal was to significantly extend the life of the drive. This is so cheaper, lower quality NAND can be used without compromising drive longevity making for cheaper SSDs. I reckon the fact that it benches really fast in benchmarks using compressible data is likely nothing more than a nice side effect.

Yes, a 64GB SandForce SSD will only show 64GB of usable space but this isn't because of an inherent limitation in the way Windows addresses the drive. It's just because that's the way the drive presents itself to the system. The controller doesn't tell the system about extra free space that isn't getting used thanks to compression. The case will be the same if you use the drive in Linux, Mac, BSD, or what have you.
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post #5 of 7
Even if your 64GB data only take up 32GB of actual space (50% compression) on the SSD, it can't give you more space because it always has to expect the worst case of 0% compression. As said before, the compression primarily extends flash lifetime by reducing the amount of data written to the flash memory. Obviously if you would only store incompressible data, like videos, the compression doesn't help.

For some applications, like compiling large C++ projects, sandforce SSDs are great because the generated files are often quite big and very well compressible (up to 80%). For other applications, like video editing, not so much. A windows installation would be somewhere in between, having an average compression ratio of maybe 30%.
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post #6 of 7
Quote:
Originally Posted by rui-no-onna View Post

Actually, I do believe the goal was to significantly extend the life of the drive. This is so cheaper, lower quality NAND can be used without compromising drive longevity making for cheaper SSDs. I reckon the fact that it benches really fast in benchmarks using compressible data is likely nothing more than a nice side effect.

Could have been.
Quote:
Originally Posted by rui-no-onna View Post

Yes, a 64GB SandForce SSD will only show 64GB of usable space but this isn't because of an inherent limitation in the way Windows addresses the drive. It's just because that's the way the drive presents itself to the system. The controller doesn't tell the system about extra free space that isn't getting used thanks to compression. The case will be the same if you use the drive in Linux, Mac, BSD, or what have you.

"There is no way to use this as additional storage space because of the way an OS addresses LBA space. Operating systems recognize a static, not a dynamic, LBA."
-http://www.tomshardware.com/reviews/vertex-3-sandforce-ssd,2869-3.html
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post #7 of 7
Quote:
Originally Posted by TopGunSF View Post

"There is no way to use this as additional storage space because of the way an OS addresses LBA space. Operating systems recognize a static, not a dynamic, LBA."
-http://www.tomshardware.com/reviews/vertex-3-sandforce-ssd,2869-3.html

You made it sound as if it's a flaw in Windows when it wasn't (all consumer desktop operating systems would treat SandForce drives the same way). Besides, all that dynamic allocation is under the hood stuff handled by the SandForce controller (and other SSD controllers for that matter) because operating systems expect a static LBA. Basically, operating systems expect something that works like a hard drive (at least as far as addressing and all that is concerned) so SSD controllers were designed to handle a bunch of under the hood stuff while presenting something that looks like an HDD to the OS.
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