I bought a samsung 840 pro 250 GB ssd ~two months ago, and I was wondering how much has been written to it. Actually, I have four partitions: /,/home,boot, and swap. To figure out how much was written to home, I wrote

$cat /sys/fs/ext4/sda7/lifetime_write_kbytes

the output was 8,985,606,440 (I added the commas). So that's 8TB. I was wondering to myself, boy I must be writing a lot. I wonder how? I monitored how much I wrote from browsing the internet and other common tasks, then I remembered that I set up a daily cron to do fstrim, because the internet told me to. So I ran

$sudo fstrim -v /home

and the output was 606,591,360 bytes were trimmed.

Then I ran

$cat /sys/fs/ext4/sda7/lifetime_write_kbytes

again and sure enough I get 8,986,209,516. So my writes increased 600MB. Now this is not really enough to account for 8TB of writes, but I had just run fstrim a few minutes earlier, so I think fstrim usually trims a lot more than 600 MB. I will have to confirm this.

Regardless, do the writes caused by fstrim actually count towards decreasing the life of your SSD? I had the impression they didn't.


I don't have to guess how much is typically trimmed by the cron job. It turns out the internet told me to log the output of fstrim. Looking at the log, I see it trimmed an average of about 150 GB/day since Aug 24, 150 GB/day * 60 days is about 9 TB. So I think the fstrim does account for the 9TB of writes I have to my SSD.

Edit 2

smart was not enabled on the SSD, but I ran $sudo smartctl -s on /dev/sda7. Then I ran $sudo smartctl -a /dev/sda7. This was the output:

smartctl 5.43 2012-06-30 r3573 [x86_64-linux-3.8.0-25-generic] (local build)
Copyright (C) 2002-12 by Bruce Allen, http://smartmontools.sourceforge.net

Device Model:     Samsung SSD 840 PRO Series
Serial Number:    S1ATNSAD780426K
LU WWN Device Id: 5 002538 5a00ae961
Firmware Version: DXM05B0Q
User Capacity:    256,060,514,304 bytes [256 GB]
Sector Size:      512 bytes logical/physical
Device is:        Not in smartctl database [for details use: -P showall]
ATA Version is:   8
ATA Standard is:  ATA-8-ACS revision 4c
Local Time is:    Wed Oct 30 09:43:18 2013 CDT
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x00) Offline data collection activity
                    was never started.
                    Auto Offline Data Collection: Disabled.
Self-test execution status:      (   0) The previous self-test routine completed
                    without error or no self-test has ever 
                    been run.
Total time to complete Offline 
data collection:        (53956) seconds.
Offline data collection
capabilities:            (0x53) SMART execute Offline immediate.
                    Auto Offline data collection on/off support.
                    Suspend Offline collection upon new
                    No Offline surface scan supported.
                    Self-test supported.
                    No Conveyance Self-test supported.
                    Selective Self-test supported.
SMART capabilities:            (0x0003) Saves SMART data before entering
                    power-saving mode.
                    Supports SMART auto save timer.
Error logging capability:        (0x01) Error logging supported.
                    General Purpose Logging supported.
Short self-test routine 
recommended polling time:    (   2) minutes.
Extended self-test routine
recommended polling time:    (  20) minutes.
SCT capabilities:          (0x003d) SCT Status supported.
                    SCT Error Recovery Control supported.
                    SCT Feature Control supported.
                    SCT Data Table supported.

SMART Attributes Data Structure revision number: 1
Vendor Specific SMART Attributes with Thresholds:
  5 Reallocated_Sector_Ct   0x0033   100   100   010    Pre-fail  Always       -       0
  9 Power_On_Hours          0x0032   099   099   000    Old_age   Always       -       458
 12 Power_Cycle_Count       0x0032   099   099   000    Old_age   Always       -       28
177 Wear_Leveling_Count     0x0013   099   099   000    Pre-fail  Always       -       2
179 Used_Rsvd_Blk_Cnt_Tot   0x0013   100   100   010    Pre-fail  Always       -       0
181 Program_Fail_Cnt_Total  0x0032   100   100   010    Old_age   Always       -       0
182 Erase_Fail_Count_Total  0x0032   100   100   010    Old_age   Always       -       0
183 Runtime_Bad_Block       0x0013   100   100   010    Pre-fail  Always       -       0
187 Reported_Uncorrect      0x0032   100   100   000    Old_age   Always       -       0
190 Airflow_Temperature_Cel 0x0032   072   068   000    Old_age   Always       -       28
195 Hardware_ECC_Recovered  0x001a   200   200   000    Old_age   Always       -       0
199 UDMA_CRC_Error_Count    0x003e   100   100   000    Old_age   Always       -       0
235 Unknown_Attribute       0x0012   001   001   000    Old_age   Always       -       4294967148
241 Total_LBAs_Written      0x0032   099   099   000    Old_age   Always       -       748699270

SMART Error Log Version: 1
No Errors Logged

SMART Self-test log structure revision number 1
No self-tests have been logged.  [To run self-tests, use: smartctl -t]

SMART Selective self-test log data structure revision number 1
    1        0        0  Not_testing
    2        0        0  Not_testing
    3        0        0  Not_testing
    4        0        0  Not_testing
    5        0        0  Not_testing
  255        0    65535  Read_scanning was never started
Selective self-test flags (0x0):
  After scanning selected spans, do NOT read-scan remainder of disk.
If Selective self-test is pending on power-up, resume after 0 minute delay.
  • How often do you hit swap? If the answer is "more than almost never", that could easily account for your counts. Commented Oct 30, 2013 at 14:16
  • 3
    My guess is that the TRIM commands sent by fstrim are being counted as writes by the ext4 driver, even though they aren't actually writes. What does SMART say? Run smartctl -a /dev/sdsa7 (you may have to install smartmontools first) and look at the Host_Writes* and NAND_Writes* fields. Commented Oct 30, 2013 at 14:26
  • 1
    Samsung doesn't report actual nand writes in SMART. You can only incraese the lifespan of your drive by trimming, because it allows the controller to arrange writes more evenly. (Well, on the other hand, Samsung Magician in Windows does somehow show a value named "Total Bytes Written", but I am not sure where it gets it from.)
    – vgru
    Commented Oct 30, 2013 at 16:01
  • 1
    So it's looking like the answer is that fstrim does not wear out your ssd; on the contrary, it increases its lifespan. The writes reported in lifetime_write_kbytes refer to file system writes at a higher abstraction level and don't necessarily correspond to physical writes to the drive. Commented Oct 30, 2013 at 16:28
  • 1
    Here a guy writes 3 PB to a 128GB Samsung 840 PRO before it dies. Sounds reassuring. Commented May 27, 2014 at 15:26

2 Answers 2


fstrim does not wear out your ssd; on the contrary, it increases its lifespan. The writes reported in lifetime_write_kbytes refer to file system writes at a higher abstraction level and don't necessarily correspond to physical writes to the drive. So although there are 40 TB of writes reported in lifetime_write_kbytes, running $sudo smartctl -s on /dev/sda7 followed by $sudo smartctl -a /dev/sda7 reveals that I have only written 750,000,000 blocks of 512 bytes each, which comes out to 375GB, which is a more reasonable value for two months of use.


trims are counted as writes in lifetime_write_kbytes as well as in all other Linux level statistics I know of, like iostat or sar, see posting. The write statistics is easily dominated by trims counted as writes, especially for moderately filled file systems.

In other words: lifetime_write_kbytes is not a reliable estimate for the amount of data written to a SSD disk.

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