sandforce compression ratio ?

[Soulkeeper]

I was looking for some numbers on measured transparent compression ratios for the hardware (not software/filesystem).

IE: install your OS on a sandforce SSD measure used space and compare to same installed files on a different drive.

Has anyone done/seen this ?

 

[Engineer]

How would the OS know the difference? It's transparent to the OS, is it not? What would you use to measure how much space it being taken up?

 

[F1shF4t]

Just have to look at the ratio of host to NAND writes in SMART. I can't remember if I've seen any article go into depth on the compression ratios though.

As far as files and used space as reported to the OS it will be the same. All the NAND space saved by compression is used as spare area by the controller, it's completely transparent to the OS.

 

[Soulkeeper]

I don't own a sandforce drive, this is why I'm asking.

I guess the drive would report the uncompressed size to the os for files, but there should be space savings from what I gather.

 

[Fred B]

The compresion rate looks not a fixed numder , when looking benchmarks from sandforce compressed and not compresed they are not the same . With CDM 0 fil it always writes with advertised performance , but with ASSD it can not be compressed there is the difference with several SD. ssd brands.
With NTFS compresion it is clear to see what file is compressed and the amount of compresion used for the file.

 

[F1shF4t]

I don't own a sandforce drive, this is why I'm asking.

I guess the drive would report the uncompressed size to the os for files, but there should be space savings from what I gather.

As I said in the post above, the OS has no knowledge of the compression, it is all internal to the drive.

For example if you write 50GB of data to a 120GB sandforce SSD the OS will see that 50GB out of 120GB is used.
Internally say the data was compressible and only 30GB was written to NAND. That means due to that compression you got higher write speeds (For 120GB sandforce SSD the write speed will range from 120MB/s to 450MB/s depending on how compressible the data is), less NAND writes and the controller has that extra 20GB that it can use as spare area. The OS will not be able to see or use that 20GB saved from compression.

 

[Soulkeeper]

So absolutely no space saving abilities offered by the sandforce compression ?
It would be neat to buy a 120GB drive and be able to put 160 or 180+ GB of files on it.
ok, thanks

 

[Engineer]

Just have to look at the ratio of host to NAND writes in SMART. I can't remember if I've seen any article go into depth on the compression ratios though.

As far as files and used space as reported to the OS it will be the same. All the NAND space saved by compression is used as spare area by the controller, it's completely transparent to the OS.

Would that take into account TRIM or garbage collection? What about cluster size? The cluster / sector size (inside the drive) would have to be the same for the various controllers to get an accurate reading?

 

[F1shF4t]

Would that take into account TRIM or garbage collection? What about cluster size? The cluster / sector size (inside the drive) would have to be the same for the various controllers to get an accurate reading?

As far as I know those SMART attributes just show the number of writes as issued to the SSD by the OS and the number of writes the controller has done to NAND. The ratio is called write amplification BTW, and sandforce is the only controller where it can be less than 1. (other controllers/brands show different SMART attributes. Samsung will show the average write cycles and the total writes, Crucial just shows the average write cycles)

I've had sandforce SSDs which were showing anywhere from 0.6 WA to 1.1 WA. All other SSDs will have WA >1.

TRIM and garbage collection would have an effect on WA (net should be to reduce WA), for other things I don't know.

 

[F1shF4t]

So absolutely no space saving abilities offered by the sandforce compression ?

Yep

It would be neat to buy a 120GB drive and be able to put 160 or 180+ GB of files on it.
ok, thanks

You can still use file system compression, but then sandforce is a terrible choice as you would not be able to take advantage of its compressible read/write speeds.