Understanding SSD Life
This is to get an idea about the life remaining of the SSD on my laptop to make sure that I am prepared enough if I were to be hosting something that does not have enough backups
So, firstly, we will look at the SMART data that the drive spits out:
$ sudo smartctl -a /dev/sda smartctl 7.2 2020-12-30 r5155 [x86_64-linux-5.14.15-arch1-1] (local build) Copyright (C) 2002-20, Bruce Allen, Christian Franke, www.smartmontools.org === START OF INFORMATION SECTION === Model Family: Samsung based SSDs Device Model: Samsung SSD 860 EVO 250GB Serial Number: SXXXXXXXXXXXXXL LU WWN Device Id: 5 0xxxx8 exxxxxxxc Firmware Version: RVT02B6Q User Capacity: 250,059,350,016 bytes [250 GB] Sector Size: 512 bytes logical/physical Rotation Rate: Solid State Device Form Factor: 2.5 inches TRIM Command: Available, deterministic, zeroed Device is: In smartctl database [for details use: -P show] ATA Version is: ACS-4 T13/BSR INCITS 529 revision 5 SATA Version is: SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s) Local Time is: Sat Nov 6 21:41:05 2021 IST SMART support is: Available - device has SMART capability. SMART support is: Enabled === START OF READ SMART DATA SECTION === 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: ( 0) seconds. Offline data collection capabilities: (0x53) SMART execute Offline immediate. Auto Offline data collection on/off support. Suspend Offline collection upon new command. 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: ( 85) 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: ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 5 Reallocated_Sector_Ct 0x0033 100 100 010 Pre-fail Always - 0 9 Power_On_Hours 0x0032 097 097 000 Old_age Always - 14016 12 Power_Cycle_Count 0x0032 099 099 000 Old_age Always - 691 177 Wear_Leveling_Count 0x0013 098 098 000 Pre-fail Always - 34 179 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 Uncorrectable_Error_Cnt 0x0032 100 100 000 Old_age Always - 0 190 Airflow_Temperature_Cel 0x0032 061 038 000 Old_age Always - 39 195 ECC_Error_Rate 0x001a 200 200 000 Old_age Always - 0 199 CRC_Error_Count 0x003e 100 100 000 Old_age Always - 0 235 POR_Recovery_Count 0x0012 099 099 000 Old_age Always - 623 241 Total_LBAs_Written 0x0032 099 099 000 Old_age Always - 9752441688 SMART Error Log Version: 1 No Errors Logged SMART Self-test log structure revision number 1 Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error # 1 Extended offline Completed without error 00% 69 - # 2 Short offline Completed without error 00% 67 - SMART Selective self-test log data structure revision number 1 SPAN MIN_LBA MAX_LBA CURRENT_TEST_STATUS 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 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.
The important things to note in this are:
Understanding Wear Leveling
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 177 Wear_Leveling_Count 0x0013 098 098 000 Pre-fail Always - 34
Every Cell in an SSD is rated for a limited number of write/erase cycles. This value tracks the average number of writes/erase cycles across the SSD.
The value will start at 100 and will slowly decrease to 0. The
RAW_VALUE is the real count or write/erase cycles.
We can see in the above data that the present
VALUE is at 98, which means we have used up 2% of the max cycles.
We can estimate the maximum number of cycles from this by assuming the
RAW_VALUE corresponds to 2%.
2 corresponds to 34 100 corresponds to x x = 34 / 2 * 100 = 1700
This assumes a linear relationship between the formula used to calculate
RAW_VALUE which might not always be the case.
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 241 Total_LBAs_Written 0x0032 099 099 000 Old_age Always - 9752441688
TBW (Tera Bytes Written) is another metric that can be used to gauge the health of your SSD by comparing it with what the manufacturer warrants it against.
For this drive, from , we can easily find that Samsung warrants this drive for 5 Years or 150 TBW. What that means that, if you have written 150TB to the drive, even if you might have done it in under 5 years, the drive will not be covered under warranty.
To make sense of that number, let us first understand where our drive stands based on the
All SSD operations happen on a block of fixed size. For our SSD, the block size is also output as part of the SMART data
Sector Size: 512 bytes logical/physical
So, each block equals 512 bytes. Which means 2 blocks equal 1kB. With this info, it will be easy to find the amount of bytes that have been written to our drive by simple math
9752441688 blocks = 9752441688 / 2 kB = 9752441688 / 2 / 1024 MB = 9752441688 / 2 / 1024 / 1024 GB 9752441688 / 2 / 1024 / 1024 GB = 9752441688 / 2 / 1024 / 1024 / 1024 TB = 4.54 TB
So, we have written 4.54 TB of data to our drive. Can we check if this data also aligns with the
Wear_Leveling_Count attribute that we checked in the previous section?
150 TB correspond to 100 4.54 TB correspond to x x = 4.54 / 150 * 100 x = 3.03
So, we are pretty close to the 2% that is reported by
Wear_Leveling_Count and the 1% can easily be due to rounding errors or other tolerances in the formula being used internally to calculate