How much my ssd is safe for use? wear level is 90%

i have a Samsung SSD 840 EVO 1TB and health is 91% and short and long test finished with success and this is my smart info :

 5 Reallocated_Sector_Ct 0x0033 100 100 010 Pre-fail Always - 0 9 Power_On_Hours 0x0032 094 094 000 Old_age Always - 28617 12 Power_Cycle_Count 0x0032 099 099 000 Old_age Always - 22 177 Wear_Leveling_Count 0x0013 091 091 000 Pre-fail Always - 97 179 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 076 055 000 Old_age Always - 24 195 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 - 13 241 Total_LBAs_Written 0x0032 099 099 000 Old_age Always - 197448746923
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Samsung(R) SSD Magician DC Version 1.0
Copyright (c) 2014 Samsung Corporation
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| Disk | Model | Serial | Firmware | Capacity | Drive | Total Bytes |
| Number | | Number | | | Health | Written |
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|0:0:1 |Samsung SSD 840 EVO 1TB |S1D9NSAF64 |EXT0BB6Q | 931 GB | GOOD | 91.97 TB |
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i want know how much is it safe? can i use it until the health is under 50% with safety ? thanks,

1 Answer

The first rule of data storage is to always have a backup. You could have a brand new SSD with a WLC of 100 and it could still fail at any time, without any warning.

The second rule of data storage is to follow the first rule.

See where I'm going with this?

In theory, the drives are supposed to be good until WLC hits 0.

• Some drives are supposed to switch to read-only mode (or die) when the MWI (Media Wearout Indicator) hits 0.

• Other drives, particularly Samsung ones, might continue working long after the WLC (Wear Leveling Count, similar property under a different name) reaches 0.

• Still other drives will simply die randomly before ever hitting 0. This can happen to any brand, any model, any drive.¹

At the end of the day, with a WLC of 91, you're probably fine for a good long while. It's supposed to be fine until at least 0. But, if you care about your data at all, make sure you have a backup.

¹ This is because MWI/WLC can only measure expected NAND degradation, which allows a lifespan estimate. However, there are other failure modes: there could be a manufacturing defect in the NAND chip or even the drive controller, there could be damage caused by higher-than-expected temperatures, any number of things could cause a drive to fail before its expected lifespan.

Back when SSDs were new, controller failures were fairly common, and happened spontaneously - no warning whatsoever. The situation is better these days, but it still happens. It's a common assumption that just because SSDs are more robust than HDDs, they're "safe" - but that's not true.