I have had a Mid 2013 13" Macbook Air for a couple of years but have barely used it as I am more of a Windows person. However, one of the things that has bothered me a bit since owning it is that the Unexpected Power Loss Count attribute on the SSD is constantly spiking, going up by several thousand per hour. It makes no difference whether the laptop is plugged in or not.

I have disabled the Put hard disks to sleep when possible and I think it may have reduced the problem a little but I'm not 100% sure.

Currently I am running OS X 10.9 Mavericks. The SSD is listed as Apple SSD SD0128F which is known to be a SanDisk model. Here is the data from an app called SSD health:

SMART data

Disk Utility has similar values although they are displayed in hexadecimal.

Whilst I realise that the raw values are not necessarily something to trust, it is nevertheless my understanding that increasing values for this attribute can indicate some kind of problem and can indicate a risk of data loss. Certainly this seems to be the case on Windows machines where the raw value is normally kept very low and associated with machines not being shut down properly or a driver issue.

I was hoping someone with a Macbook Air and similar Sandisk SD0XXXF type SSD could check their data to compare it to mine. The laptop is coming up to the end of its two year warranty so if there is an issue I would like to get it fixed soon.

1 Answer 1


Fundamentally the SMART data of your 2013 Macbook Air SSD is normal comparing it with my Apple SSD SD0128F (inside a Fusion drive).

Probably some attribute names (namely Unexpected Power Loss Count and Program Fail Count Chip) provided by your SMART app are false: Using two different SMART utilities here, the ID# 174 has the attribute name Host_Reads_MiB and the ID# 175 has the attribute name Host_Writes_MiB in both applications, which mean all read / written Mebibytes (~ 1.05 MB) in the life time of the SSD.

In your case that would translate to ~773 GB read and ~367 GB written. Considering 3 power on hours (ID 9) of the SSD this results in 71.6 MB/s read and 33.9 MB/s written constantly - which seems a bit high.

The values here are 14,894,386 and 20,658,326 which equal 15.6 TB read and 21,7 TB written. With 698 power on hours this results in 6.2 MB/s read and 8.6 MB/s written constantly.

You may test this by making notes of the two values (ID174/175), executing a full restart and comparing the new values with the old values:

In my case (Mavericks 10.9.5) on the SSD the ∆ host_reads_MiB is 1820 MB and the ∆ host_writes_MiB 291 MB. On the HDD the ∆ Total_LBA_READ is 475 MB and the ∆ Total_LBA_Written 22 MB. Taken together ~2.3 GB are read and 313 MB are written while restarting a Mac - which seem legit values.

  • The Power on Hours seems to be completely wrong on mine, the laptop has probably been used by me for 30-40 hours. It seems like the drive is being put to standby all the time to save power even on AC power with the Put hard disks to sleep when possible setting disabled. Which SMART utility are you using BTW?
    – James
    Jun 12, 2015 at 10:43
  • @James SMARTReporter and SMART Utility. The power on hours value on my Mac seems valid. The HDD part of the Fusion Drive shows ~7600 hours (317 days).
    – klanomath
    Jun 12, 2015 at 10:49
  • @James BTW "Power on hours" in this context doesn't mean "Power on hours" of the Mac but "Power on hours" of the SSD itself!
    – klanomath
    Jun 12, 2015 at 11:27
  • I think you are right, it seems that the display names of attribute 174 and 175 are wrong and it is because the ID's are not actually unique. This would also explain why the health values are still at 100 despite the high raw values. Still I would have expected Apple to at least have made an effort to get it right in the Disk Utility since they don't exactly support a lot of SSD's officially.
    – James
    Jun 12, 2015 at 12:46
  • I had some problems with several applications not installing correctly shortly after I first got the Mac which was one of the things that had made me concerned that there was a hardware problem. However, I think it may have been down to a bad internet connection and hopefully the issue has gone away.
    – James
    Jun 12, 2015 at 12:51

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