Another Linux user data point: XPS13(9310)/512GB nvme/16GB RAM/2GB swapfile/kubuntu 20.10/kernel 5.11 (in use since ~Dec 5, 2020):

  SMART/Health Information (NVMe Log 0x02)
  Critical Warning:                   0x00
  Temperature:                        33 Celsius
  Available Spare:                    100%
  Available Spare Threshold:          50%
  Percentage Used:                    0%
  Data Units Read:                    631,319 [323 GB]
  Data Units Written:                 1,157,883 [592 GB]
  Host Read Commands:                 4,650,820
  Host Write Commands:                7,329,774
  Controller Busy Time:               16
  Power Cycles:                       37
  Power On Hours:                     45
  Unsafe Shutdowns:                   15
  Media and Data Integrity Errors:    0
  Error Information Log Entries:      1
  Warning  Comp. Temperature Time:    0
  Critical Comp. Temperature Time:    0

I do Linux kernel dev and have done quite a few kernel compiles at this point (using Ubuntu's full config) as well as general browsing and some Docker workloads and Spotify... Judging by 'Power On Hours' combined with 'Data Units Written', looks like there's a bug to me.

As a side, I don't know why 'Available Spare Threshold' is 50%, and the 1 'Error Information Log Entries' appears to be successful results of some test.

I have the same question here. How do you only have 45 power on hours in 80 days?

Does anyone know why power on hours seem to be under reported so often?

On linux there are a bunch of "laptop mode" configurations that can minimize the time the disk will be woken up to actually write out data. The price is that you'll lose the last N minutes of work on a hard crash. And it only works when you have enough RAM to avoid swapping and keep dirty pages in memory. And your workloads don't explicitly call fsync. But if setup correctly your drive will spend most of its time sleeping.

> And your workloads don't explicitly call fsync.

If you run ZFS, you can set sync=disabled for your filesystems. This will disable fsync.

Unlike most (all?) other filesystems, that's actually safe. ZFS doesn't reorder writes between transaction groups, so after a crash you'll get a consistent state from however many minutes ago.

(However, txgs have a time limit of 5 seconds by default. You also need to increase that.)

As it relates to the Mac's, I'm starting to wonder if their SMART reporting is just faulty. Power on Hours seems to be definitively wrong, I'm starting to wonder if all of the SMART data is bogus and there is no issue.

Just a guess, but maybe it doesn't count time in low power modes?

Another Linux datapoint, X1 Carbon 6th Generation, daily use.

  SMART/Health Information (NVMe Log 0x02)                                                                                                                                                            
  Critical Warning:                   0x00   
  Temperature:                        35 Celsius
  Available Spare:                    100%
  Available Spare Threshold:          10%                                                           
  Percentage Used:                    25%
  Data Units Read:                    22,242,132 [11.3 TB]
  Data Units Written:                 74,693,212 [38.2 TB]
  Host Read Commands:                 540,582,518                                                   
  Host Write Commands:                1,857,635,922                            
  Controller Busy Time:               5,131                                                         
  Power Cycles:                       884                                                           
  Power On Hours:                     3,497                                                                                                                                                           
  Unsafe Shutdowns:                   261                                                           
  Media and Data Integrity Errors:    0      
  Error Information Log Entries:      882       
  Warning  Comp. Temperature Time:    0         
  Critical Comp. Temperature Time:    0        
  Temperature Sensor 1:               35 Celsius
  Temperature Sensor 2:               37 Celsius

How do you only have 558 PoH with ~900 days of daily use? Do you only use it for 30m per day?

Here's a 512GB WD Black from my home lab server. It runs ~10 super light usage VMs with Docker stacks that include 2 GitLab instances, 2 GitLab runners, 3 Nextcloud instances, 3 Redmine instances, 1 Gitea instance, 2 Drone runners, 1 Minio instance, 1 Nexus instance, 1 Emby instance (w/transcoding), and various reverse proxies, etc..

The write endurance is supposed to be 300TBW, so it should really be over 20% used but says 0%.

    SMART/Health Information (NVMe Log 0x02)
    Critical Warning:                   0x00
    Temperature:                        38 Celsius
    Available Spare:                    100%
    Available Spare Threshold:          10%
    Percentage Used:                    0%
    Data Units Read:                    95,066,245 [48.6 TB]
    Data Units Written:                 135,910,315 [69.5 TB]
    Host Read Commands:                 972,466,473
    Host Write Commands:                2,504,003,547
    Power On Hours:                     17,383

    Error Information (NVMe Log 0x01, max 256 entries)
    No Errors Logged

Compare it to a 500MB Crucial MX500 under the same load which is supposed to have 180TBW:

    Model Family:     Crucial/Micron BX/MX1/2/3/500, M5/600, 1100 SSDs
    Device Model:     CT500MX500SSD1
    Serial Number:    
    Sector Sizes:     512 bytes logical, 4096 bytes physical
    Rotation Rate:    Solid State Device
    Form Factor:      2.5 inches

    ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
    9   Power_On_Hours          0x0032   100   100   000    Old_age   Always       -       11225
    173 Ave_Block-Erase_Count   0x0032   032   032   000    Old_age   Always       -       1032
    194 Temperature_Celsius     0x0022   067   044   000    Old_age   Always       -       33 (Min/Max 0/56)
    202 Percent_Lifetime_Remain 0x0030   032   032   001    Old_age   Offline      -       68
    246 Total_Host_Sector_Write 0x0032   100   100   000    Old_age   Always       -       59166051308

That's 68% used after ~30TBW (59,166,051,308 sectors*512 = 30,293,018,269,696 bytes).

What I've learned from trying to diagnose those MX500s is that TBW doesn't really matter all that much. It's the P/E cycles that really count. For example, the MX500s are rated for 1500 erase cycles (#173 above) IIRC.

I've also become skeptical of many SMART implementations. I know the PoH on the Crucials is incorrect because when they were new they were reporting 45 days of PoH on a system with 76 days of uptime. So if the manufacturers can't get something as simple as PoH right, how can anything be trusted?

I have a 1TB MX500 and a much older 240GB M500 and the PoH stats are similarly unrealistic for both. The MX500 has ran close to 24/7 for two months now and reports 328h which is like 14 days. The M500 reports 12k hours (~1.35 years) but it's 5+ years old and I'm sure it should be higher.

OTOH the number of power cycles they report seem to be too high, at 45 and 2332 respectively. Maybe that's related?

I have a different work laptop so I mostly use this on weekends and weeknights and I believe NVME APST mode may be affecting it.

Then there's always the possibility of wrong interpretation of the numbers as every OEM has possibly different implementation.

In Apple's case it's more likely they have the right implementation as they make both the software and the hardware. There could still be bugs..