My understanding is that Reallocated_Sector_Ct gives the absolute number of remapped sectors while Reallocated_Event_Count gives the number of tries to initiate such a remapping. How could it then by that a disk has a Reallocated_Sector_Ct of 0 but thousands of Reallocated_Event_Count such as this Seagate ST9500420AS:

  5 Reallocated_Sector_Ct   0x0033   100   100   036    Pre-fail  Always       -       0
196 Reallocated_Event_Count 0x000f   087   087   030    Pre-fail  Always       -       11481 (35561 0)

I seriously doubt that there were 11481 unsuccessful attempts to map sectors on this drive. If I would have to guess then I would say that the interpretation of these values on the interwebs does not reflect what the vendors' or at least Seagate's engineers implemented :) Is there a better explanation?

  • Interesting! I once had a hard drive whose Reallocated_Event_Count suddenly started going up while Reallocated_Sector_Ct stayed at 0. This was a laptop, I can't be 100% sure but I think it was a Seagate drive too. I agree with you -- it seems unlikely that all attempts to reallocate would fail. I bet Reallocated_Sector_Ct is just not implemented in this drive or Seagate are using SMART attributes in some proprietary way. – misha256 Mar 20 '17 at 1:37
  • From my observations with several damaged Seagate drives Reallocated_Event_Count may also rise while reading damaged sectors. Reallocating at least under linux doesn't occur while reading, it occurs only when writing and then Reallocated_Sector_Ct rises, if there's still space in spare area. But I may be completely wrong. – Michal Sokolowski Apr 12 '17 at 18:24

The most likely explanation is that Seagate uses SMART attributes in a proprietary way.

Seagate has this to say:

The SMART values that might be read out by third-party SMART software are not based on how the values may be used within the Seagate hard drives. Seagate does not provide support for software programs that claim to read individual SMART attributes and thresholds...

...some third-party SMART software programs display a list of attributes that seem to announce or foreshadow a SATA hard drive failure... please remember that these third-party programs do not have proprietary access to Seagate hard disk information, and therefore often provide inconsistent and inaccurate results. SeaTools is more consistent and more accurate and is the standard Seagate uses to determine hard drive failure.

Seems like Seagate is quite happy to use the SMART attributes any way it wants to.


Is there a better explanation?

Unsuccessful attempts are counted as well as successful.

9132: S.M.A.R.T. Attribute: Reallocation Event Count

Attribute ID: 196 (0xC4) Hard drives, supporting this attribute

Samsung, Seagate, IBM (Hitachi), Fujitsu (not all models), Maxtor, Western Digital (not all models)


Reallocation Event Count S.M.A.R.T. parameter indicates a count of remap operations (transferring data from a bad sector to a special reserved disk area - spare area).

The raw value of this attribute shows the total number of attempts to transfer data from reallocated sectors to a spare area. Unsuccessful attempts are counted as well as successful. Since this is a count value, it can only increase.


This is a critical parameter. Degradation of this parameter may indicate imminent drive failure. Urgent data backup and hardware replacement is recommended.

Source 9132: S.M.A.R.T. Attribute: Reallocation Event Count

  • I mentioned that in my question... – stefanct Mar 19 '17 at 23:47
  • @stefanct If your disk is failing then 11481 failed attempts is certainly possible. – DavidPostill Mar 19 '17 at 23:49

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