Total Bytes Written Weirdness

Piyono

Storage is cool
Joined
Jan 25, 2002
Messages
548
Location
Toronto
Today—on a whim—I checked one of my NVMe drives (WD Blue 1TB) to see how it was wearing.
The WD Dashboard app doesn't show TBW but it reports SMART data.
The value it shows is "3340658 Data Units Written", which I took to mean "Total LBA written".

The problem with 3,340,658 x 512 LBA sectors written is that it translates to 1.631GiB, which can't be the case because I've filled nearly the entire 1TB capacity of the drive.

I used a couple of other SMART checkers and they all report the same figure.

I also double-checked and the drive is using 512-byte logical sectors.

Any ideas as to what's up?
 

LunarMist

I can't believe I'm a Fixture
Joined
Feb 1, 2003
Messages
15,514
Location
USA
The newer NVMe drives such as Samsung and WD have mystical SMART data. It's really BS.
My WD SSDs in a laptop both indicate 100% remaining life in the Dashboard, but they each have a rating of 5100 TBW so it may take awhile.
Is the granularity of % insufficient to mange your drive?
 

Piyono

Storage is cool
Joined
Jan 25, 2002
Messages
548
Location
Toronto
The newer NVMe drives such as Samsung and WD have mystical SMART data. It's really BS.
My WD SSDs in a laptop both indicate 100% remaining life in the Dashboard, but they each have a rating of 5100 TBW so it may take awhile.
Is the granularity of % insufficient to mange your drive?
This all started when I asked a seller on Kijiji to post a screenshot of the TBW of a Western Digital SSD.
I figured it would be right there in the overview page or the SMART data. Nope.

I guess the cryptic health score is fine, but it's puzzling (and a little irritating) that WD would obscure such basic information.
 

LunarMist

I can't believe I'm a Fixture
Joined
Feb 1, 2003
Messages
15,514
Location
USA
It's not really SMART data when it is proprietary, but maybe that changed with NVMe. I noticed a few years ago that SMART software wasn't correct when used on Samsung 900 series SSDs.
 

Chewy509

Wotty wot wot.
Joined
Nov 8, 2006
Messages
3,229
Location
Gold Coast Hinterland, Australia
The value it shows is "3340658 Data Units Written", which I took to mean "Total LBA written".
IIRC, Data Units is the NAND cell size, you'll have to find what NAND is used and find out what size cells it's using as the physical size to determine the correct value. (typically it's 4KB, but I have seen some that are 8KB or 16KB in the wild).

As a best guess, it'll be 4K sectors (The NVMe information should give you the physical sector size), so that'll be 13GB written, which doesn't make sense. If you've written 1TB, then that means the Data Unit size is 321KB, which to the nearest base 2 would be 256KB for a Data Unit.

Again that doesn't make sense, as Kingston notes they determine the Data Unit to be the physical sector size. (surely WDC is not using huge physical sizes like that)?

And the SMART attributes notes the value is 16 bytes (128bits) in size, so it's unlikely to be a integer overflow issue?

Something tells me either WDC firmware has issues, or the software reading the value is wrong. Alternatively could this value be from last power on? (surely not)?

Have you tried Crystal Disk Info to see what it says?
 

LunarMist

I can't believe I'm a Fixture
Joined
Feb 1, 2003
Messages
15,514
Location
USA
Are you assuming the count is for blocks or pages? IIRC a block could be 1MB more or less.
 

Piyono

Storage is cool
Joined
Jan 25, 2002
Messages
548
Location
Toronto
Have you tried Crystal Disk Info to see what it says?
Ah, no, as a matter of fact I didn't!
Rather silly of me.

1652469116193.png


And there you have it.
Clearly the drive makes the data available for anyone who knows how to access it.
 

Chewy509

Wotty wot wot.
Joined
Nov 8, 2006
Messages
3,229
Location
Gold Coast Hinterland, Australia
I tend to prefer 3rd party tools in some cases as they deal with all the "issues" with the firmware and reporting. Since CrystalDiskInfo is open-source, you could look at the source code to determine how it works out total bytes read/written from the smart information.

So it looks like a Data Unit on the WDC is 512KB in size. (total written / data unit count).
 

Piyono

Storage is cool
Joined
Jan 25, 2002
Messages
548
Location
Toronto
I tend to prefer 3rd party tools in some cases as they deal with all the "issues" with the firmware and reporting.
Case in point.

Since CrystalDiskInfo is open-source, you could look at the source code to determine how it works out total bytes read/written from the smart information.
Yes, a hypothetical, code-literate variant of me could do that. 😁

So it looks like a Data Unit on the WDC is 512KB in size. (total written / data unit count).
Yes, that was accurately reported in Windows, but where are you seeing total written/data unit count?
 
Top