Re: Migrating system from u-sd to nvme memory on arm64's?

[Stefan Monnier <monnier@iro.umontreal.ca>]

> smartctl -a /dev/whatever produces SMART data which may include
> things like:
>
> 233 Media_Wearout_Indicator 0x0032   002   002   000    Old_age   Always       -       0
>  or
>
> 241 Total_LBAs_Written      0x0032   099   099   000    Old_age   Always       -       7395041209
>  or
>
> 177 Wear_Leveling_Count     0x0013   099   099   000    Pre-fail  Always       -       4
>
> Each of which tells you relevant things without being perfect
> predictors.

Any idea what those numbers actually mean?  Like what kind of units?
Is the `Wear_Leveling_Count` an approximation of the average number of
times are block has been (re)written?
Is an "LBA" a 512B block or a 4kB block or ...?

It's not obvious how to translate that to "30%".
Jeremy?  Do you remember what data made it possible to get this 30% estimate?

FWIW, here's the smartctl data on my current 12 year old 256GB SSD, with
swap on it (until 2 years ago, with a measly 4GB of RAM, now with 16GB):

  1 Raw_Read_Error_Rate     0x002f   199   199   000    Pre-fail  Always       -       9952
  5 Reallocated_Sector_Ct   0x0033   098   098   000    Pre-fail  Always       -       103
  9 Power_On_Hours          0x0032   098   098   000    Old_age   Always       -       9586
 12 Power_Cycle_Count       0x0032   076   076   000    Old_age   Always       -       23891
169 Unknown_Attribute       0x0013   253   253   010    Pre-fail  Always       -       8324191885568
173 Unknown_Attribute       0x0032   174   174   100    Old_age   Always       -       2431002739356
175 Program_Fail_Count_Chip 0x0032   098   098   010    Old_age   Always       -       72
176 Erase_Fail_Count_Chip   0x0032   100   100   010    Old_age   Always       -       0
177 Wear_Leveling_Count     0x0013   084   084   017    Pre-fail  Always       -       566
178 Used_Rsvd_Blk_Cnt_Chip  0x0013   076   076   010    Pre-fail  Always       -       1004
179 Used_Rsvd_Blk_Cnt_Tot   0x0013   076   076   010    Pre-fail  Always       -       1938
180 Unused_Rsvd_Blk_Cnt_Tot 0x0013   076   076   010    Pre-fail  Always       -       6382
181 Program_Fail_Cnt_Total  0x0032   098   098   010    Old_age   Always       -       103
182 Erase_Fail_Count_Total  0x0032   100   100   010    Old_age   Always       -       0
183 Runtime_Bad_Block       0x0013   098   098   010    Pre-fail  Always       -       103
187 Reported_Uncorrect      0x0032   090   090   000    Old_age   Always       -       9952
192 Power-Off_Retract_Count 0x0032   095   095   000    Old_age   Always       -       22568
194 Temperature_Celsius     0x0022   059   059   000    Old_age   Always       -       41 (Min/Max 15/63)
195 Hardware_ECC_Recovered  0x001a   001   001   000    Old_age   Always       -       9952
197 Current_Pending_Sector  0x0013   100   100   000    Pre-fail  Always       -       0
198 Offline_Uncorrectable   0x0030   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x003e   253   253   000    Old_age   Always       -       0

Apparently it's been ON for the equivalent of only 1 year :-)
Not sure what those `Unknown_Attribute` represent: the numbers are large
enough to suggest it could count the total amount written, but if it's
counted in blocks, it seems very high, so it would have to be counted in
bytes, but 8TB sounds a bit low.


        Stefan