I am trying to assess the health of my SSD drive (of a MBPr 15" mid-2014). I tried to do smartctl -a disk0, which gave the following output:

SMART Attributes Data Structure revision number: 40
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED      WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x001a   200   200   000    Old_age   Always       -       0
  5 Reallocated_Sector_Ct   0x0033   100   100   000    Pre-fail  Always       -       0
  9 Power_On_Hours          0x0032   099   099   000    Old_age   Always       -       3005
 12 Power_Cycle_Count       0x0032   097   097   000    Old_age   Always       -       2767
169 Unknown_Attribute       0x0013   253   253   010    Pre-fail  Always       -       1885834579712
173 Wear_Leveling_Count     0x0032   190   190   100    Old_age   Always       -       8609857595
174 Host_Reads_MiB          0x0022   099   099   000    Old_age   Always       -       5571155
175 Host_Writes_MiB         0x0022   099   099   000    Old_age   Always       -       6795580
192 Power-Off_Retract_Count 0x0012   099   099   000    Old_age   Always       -       49
194 Temperature_Celsius     0x0022   059   059   000    Old_age   Always       -       41 (Min/Max 16/66)
197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       0
199 UDMA_CRC_Error_Count    0x001a   200   200   000    Old_age   Always       -       0
240 Unknown_SSD_Attribute   0x0022   100   100   000    Old_age   Always       -       0

I don't understand how I can get 190 as the Wear_Leveling_Count. I'm not really sure how to interpret the other numbers either. Could you help me understand what these numbers mean?

up vote 1 down vote accepted

I believe these macbooks use samsung SSDs (correct me if I'm wrong). Here is a link to a SSD white paper from samsung explaining the SMART data.

there it says: ID # 177 Wear Leveling Count

This attribute represents the number of media program and erase operations (the number of times a block has been erased). This value is directly related to the lifetime of the SSD. The raw value of this attribute shows the total count of P/E Cycles.

However, they do not exactly explain what the columns VALUE WORST and THRESH mean. I found somewhere, that these values work as follows: "The manufacturer defines a threshold number against which the “value” is compared, and if the “value” drops below that threshold, SMART reports that attribute as FAILING_NOW, and sets the overall health as FAILED."

So I'd say a wear leveling value of 190 is perfectly fine, since it is well above the threshold of 100 (I am assuming it starts at 200 just like Raw Read Error Rate). If your macbook is one year old now, the ssd should last approximately another 9 years if you keep the same usage patterns.

Also, none of the attributes has a date in the column WHEN_FAILED, so you need not be worried, everything is fine with your SSD.

I have a MacBook Pro retina (early 2013) myself, and my smart data looks pretty similar to yours:

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
  1 Raw_Read_Error_Rate     0x001a   200   200   000    Old_age   Always       -       0
  5 Reallocated_Sector_Ct   0x0033   100   100   000    Pre-fail  Always       -       0
  9 Power_On_Hours          0x0032   098   098   000    Old_age   Always       -       5352
 12 Power_Cycle_Count       0x0032   089   089   000    Old_age   Always       -       10513
169 Unknown_Attribute       0x0013   253   253   010    Pre-fail  Always       -       2302974898688
173 Wear_Leveling_Count     0x0032   193   193   100    Old_age   Always       -       12899778635
192 Power-Off_Retract_Count 0x0012   099   099   000    Old_age   Always       -       33
194 Temperature_Celsius     0x0022   065   040   000    Old_age   Always       -       35 (Min/Max 6/60)
197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       0
199 UDMA_CRC_Error_Count    0x001a   200   200   000    Old_age   Always       -       0

The reason my Wear Leveling Count is still a little better than yours, despite the fact that my raw value is 50% higher than yours, is likely because I have a 500GB SSD which can take more writes in total than, say, a 250GB one.

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