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Read/write values on SandForce based SSD too low #364

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
Just installed OHW 0.5.1 beta (on Windows 7 x64) and noticed that it now also 
displays some read/write statistics for my SandForce-1200 based SSD (nice 
feature by the way). There's one problem though: The GB values provided appear 
to be "a bit" too low...

Apparently, the reads/writes reported by the SF-1200 controller are in 
increments of 64 GB. So in order to display (approximately) the correct values, 
the numbers returned by the drive will need to be multiplied by 64.

For further reference have a look at this list of SMART attributes for the 
SF-1200 controller (and possibly other SandForce controllers as well):
http://www.ocztechnologyforum.com/staff/ryderocz/misc/Sandforce.jpg (from: 
http://www.ocztechnologyforum.com/forum/archive/index.php/t-75786.html).

Original issue reported on code.google.com by thijsput...@gmail.com on 26 Jul 2012 at 11:29

GoogleCodeExporter commented 9 years ago 
The documentation for Kingston SF-2000 based SSDs says the following:

"This Attribute returns a byte count, in units of Gigabytes
at an update resolution of 64 GBytes. The count
represents the number of bytes written. The Attribute
reads ‘0’ until the number of bytes written reaches
64GB; at 64GB the Attribute increments to a value of ‘64’
(decimal)."

This means the value does not need to be multiplied by 64, but increments in 64 
steps only.

The documentation you have linked "number of bytes, in 64GB increments" is 
unclear as to what this really means. The above quoted documentation is a lot 
clearer about this. Now it could be that things have been different for SF-1200 
drives, but I have no data that would support this. The OCZ Vertex 2 I use as 
well gives reasonable results too.

Do you have any tests that would support your claim of too low values? Can you 
attach a report of your system?

Original comment by moel.mich on 26 Jul 2012 at 11:47

GoogleCodeExporter commented 9 years ago 
Attached the relevant parts of a report for my system.

My 250 GB SandForce-1200 based SSD (which is 60% full at the moment) has a 
"Host Writes to Controller" value of 2944... The resulting write amplification 
value seems a bit off as well, but let's take this one step at a time ;)

Original comment by thijsput...@gmail.com on 26 Jul 2012 at 12:04

Attachments:

GoogleCodeExporter commented 9 years ago 
All three numbers 4352, 2944, 5120 are a multiples of 64, which agrees with the 
documentation I quoted above.

Have you ever updated your firmware? I am not sure what counters could get 
reset by a firmware update, but this is something to consider.

I still don't see why the value of 2944 should be wrong.

Original comment by moel.mich on 26 Jul 2012 at 12:16

GoogleCodeExporter commented 9 years ago 
You're absolutely right, my bad :|

For some reason I was interpreting the numbers as being in MB instead of GB, 
causing them to not make any sense... 2944 GB (instead of MB ;) makes complete 
sense.

Anyway, sorry for the wasted effort and again thanks for a great tool!

Original comment by thijsput...@gmail.com on 10 Aug 2012 at 4:26

GoogleCodeExporter commented 9 years ago

Original comment by moel.mich on 11 Aug 2012 at 10:03