Question about my calculation for TBW. Is this the correct way?

Kilobyte Kid

Question about my calculation for TBW. Is this the correct way?

Hi all,

My Micron/Crucial SSD doesn't have Total LBAs Written (ID 241) SMART value/string.

So I looked up a few .pdf-documents and combined everything to one formula, but I have no clue if I am correct.
First I will calculate WAF by using this formula:

WAF = 1+ (248_Bckgnd_Program_Page_Cnt / 247_Host_Program_Page_Count)


And then finally using the WAF-result in the formula below to determine TBW:

TBW = ((Capacity GB/1000) x 173_Ave_Block-Erase_Count ) / WAF


I used it on my SSD drive with the following information:

 

  • 256 GB SSD
  • 248_Bckgnd_Program_Page_Cnt = 27099679202
  • 247_Host_Program_Page_Count = 4591819114
  • 173_Ave_Block-Erase_Count = 3130

 

The final result was: ~116.1 TB

Is this correct, or did I make a mistake somewhere? According to the .pdf's I found on the internet and a few forums, this should be correct, right?
If not, tell me where I am going wrong.

Thank you in advance!

 

13 Replies
JEDEC Jedi

Re: Question about my calculation for TBW. Is this the correct way?

[ Edited ]

I think this is correct.

Don't you have #F6 (ID 246) Total Host Sector Writes SMART value?

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Kilobyte Kid

Re: Question about my calculation for TBW. Is this the correct way?

Yeah I have SMART value 246.

Why?
...don't tell me there is an easier way? Smiley Tongue

JEDEC Jedi

Re: Question about my calculation for TBW. Is this the correct way?

Try this: (ID 246) x 512 / 1024 / 1024 / 1024 / 1024 to get the result in TBs.

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Kilobyte Kid

Re: Question about my calculation for TBW. Is this the correct way?

FYI: 246 Total_Host_Sector_Write 0x0032   100   100   000    Old_age   Always       -       105912412189

I tried what you said:

105912412189 x 512 / 1024 / 1024 / 1024 / 1024


However the outcode is completely different compared to what I had: ~49.32 TB compared to the ~116.1 TB I calculated from my first post? Smiley Frustrated

JEDEC Jedi

Re: Question about my calculation for TBW. Is this the correct way?

Um, could you post your SMART data? With CrystalDiskInfo use 'Edit > Copy' option, just please remove drive's serial number.

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Kilobyte Kid

Re: Question about my calculation for TBW. Is this the correct way?

Sorry not possible, it's a Linux machine running CentOS.

JEDEC Jedi

Re: Question about my calculation for TBW. Is this the correct way?

No problem, I just wanted to see all SMART values and SSD model to make sure if there is no mistake or something Smiley Wink

See the example data for Crucial M550 256GB:

 

(ID) Attribute Now Worst Value
(01) Raw read error rate 100 100 0
(05) Reallocated sector count 100 100 0
(09) Power-on hours count 100 100 6862
(0C) Power cycle count 100 100 1431
(AB) Unknown 100 100 0
(AC) Unknown 100 100 0
(AD) Unknown 97 97 92
(AE) Unknown 100 100 297
(B4) Unknown 0 0 2159
(B7) Unknown 100 100 0
(B8) Unknown 100 100 0
(BB) vendor-specific 100 100 0
(C2) HDA temperature 69 45 236224249887
(C4) Reallocation count 100 100 16
(C5) Current pending sector count 100 100 0
(C6) Offline scan uncorrectable count 100 100 0
(C7) UDMA CRC error rate 100 100 574
(CA) Data Address Mark errors 97 97 3
(CE) Flying height 100 100 0
(D2) Unknown 100 100 0
(F6) Unknown 100 100 15860476183
(F7) Unknown 100 100 501260677
(F8) Unknown 100 100 1028487346

 

For this data all the calculations, I know about, work correctly. And as far as I can remember it works for my other Crucial SSDs.

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Kilobyte Kid

Re: Question about my calculation for TBW. Is this the correct way?

I can display stuff with smartctl, here is the output:

SMART Attributes Data Structure revision number: 16
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x002f   100   100   000    Pre-fail  Always       -       2
  5 Reallocate_NAND_Blk_Cnt 0x0033   100   100   000    Pre-fail  Always       -       0
  9 Power_On_Hours          0x0032   100   100   000    Old_age   Always       -       20979
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       3
171 Program_Fail_Count      0x0032   100   100   000    Old_age   Always       -       0
172 Erase_Fail_Count        0x0032   100   100   000    Old_age   Always       -       0
173 Ave_Block-Erase_Count   0x0032   252   252   000    Old_age   Always       -       3133
174 Unexpect_Power_Loss_Ct  0x0032   100   100   000    Old_age   Always       -       2
180 Unused_Reserve_NAND_Blk 0x0033   000   000   000    Pre-fail  Always       -       2159
183 SATA_Interfac_Downshift 0x0032   100   100   000    Old_age   Always       -       0
184 Error_Correction_Count  0x0032   100   100   000    Old_age   Always       -       0
187 Reported_Uncorrect      0x0032   100   100   000    Old_age   Always       -       0
194 Temperature_Celsius     0x0022   068   062   000    Old_age   Always       -       32 (Min/Max 15/38)
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0032   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0030   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x0032   100   100   000    Old_age   Always       -       0
202 Percent_Lifetime_Used   0x0031   252   252   000    Pre-fail  Offline      -       104
206 Write_Error_Rate        0x000e   100   100   000    Old_age   Always       -       0
210 Success_RAIN_Recov_Cnt  0x0032   100   100   000    Old_age   Always       -       0
246 Total_Host_Sector_Write 0x0032   100   100   000    Old_age   Always       -       105983216107
247 Host_Program_Page_Count 0x0032   100   100   000    Old_age   Always       -       4594863312
248 Bckgnd_Program_Page_Cnt 0x0032   100   100   000    Old_age   Always       -       27146565899

Hope this helps. FYI: these values are taken just a few seconds ago, so the result might be a little different compared my previous results (which were a day old).

I still think it's weird that I come up with 2 completely different values. So I really would like to know which one is true.

Kilobyte Kid

Re: Question about my calculation for TBW. Is this the correct way?

It's a Crucial MX100 256GB forgot to mention that.