How should I understand "Current Pending Sector Count" in CrystalDiskInfo reports?

Question

My USB disks keeps showing (after each Check Disk pass) keeps informing me about new clusters added to Bad Clusters File:

but it does not list them as "damaged sectors" in disk summary:

and thus I wasn't 100% sure, if this is normal situation or if my disk is failing. I browsed through this and this questions and answers, but found no reliable answer, as both of them are asking about sectors already listed in summary as damaged.

Thus, after reading of this article I downloaded portable version of CrystalDiskInfo 6.7.5 x64 and... either I'm stupid or I completely don't understand results, that it brings to me.

I can see, that my disk results in "caution" health status, but what really surprises me is that...

... virtually every parameter, that program has analysed is above threshold and yet only one is marked with yellow color to bring my attention.

What am I missing or how should I read CrystalDiskInfo reports? Why other S.M.A.R.T. parameters are not marked as warning / dangerous / caution, of they're also above threshold?

Answer 1

What is Current Pending Sector Count and should I worry about it?

This is a "Potential indicator of imminent electromechanical failure" (row coloured pink in S.M.A.R.T.).

You should back up this disk as it could fail at any moment. Keep an eye on this value and see if it increases.

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S.M.A.R.T. Attribute: Current Pending Sector Count

Description

Current Pending Sector Count S.M.A.R.T. parameter is a critical parameter and indicates the current count of unstable sectors (waiting for remapping). The raw value of this attribute indicates the total number of sectors waiting for remapping. Later, when some of these sectors are read successfully, the value is decreased. If errors still occur when reading some sector, the hard drive will try to restore the data, transfer it to the reserved disk area (spare area) and mark this sector as remapped.

Please also consult your machines's or hard disks documentation. Recommendations

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

Source S.M.A.R.T. Attribute: Current Pending Sector Count

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• Count of "unstable" sectors (waiting to be remapped, because of unrecoverable read errors).

• If an unstable sector is subsequently read successfully, the sector is remapped and this value is decreased.

• Read errors on a sector will not remap the sector immediately (since the correct value cannot be read and so the value to remap is not known, and also it might become readable later); instead, the drive firmware remembers that the sector needs to be remapped, and will remap it the next time it's written.

  However some drives will not immediately remap such sectors when written; instead the drive will first attempt to write to the problem sector and if the write operation is successful then the sector will be marked good (in this case, the "Reallocation Event Count" (0xC4) will not be increased).

  This is a serious shortcoming, for if such a drive contains marginal sectors that consistently fail only after some time has passed following a successful write operation, then the drive will never remap these problem sectors.

Source S.M.A.R.T.

Answer 2

To provide some additional information on the question in the title:

Cause

This SMART metric is only present in classical hard drives that record data magnetically on spinning discs (called "platters") that are coated in a material suitable for the purpose.

The coating can have a weak spot or other kinds of damage can develop over time due to thermal cycling, shocks or entry of dust or condensation into the enclosure.

Usually, the hard drive electronics will not notice the problem during writing but when attempting to read data from the damaged spot. At this point, the hard drive will mark the sector as "pending" and do one of two things:

• A standard hard drive will attempt to read the sector several times (and appear unresponsive for tens of seconds) until either a read attempt is successful or the drive gives up. The operating system may itself try additional reads.

• A RAID hard drive will signal the read error right away, leaving it up to the RAID controller or operating system to either fall back to another RAID drive or perform additional read attempts.

Finally, when the new data is written to the a spot marked as "pending," that spot will be marked as "bad" and the data will instead be written to a spare location the drive keeps for this purpose. The pending sector thus becomes as "reallocated sector."

(Depending on drive, manufacturer and firmware, there can also be paths for a pending sector to become a normal sector again, for example if, after the next write to the pending sector, it can be read normally)

Recommendations

Having a small number of pending/reallocated sectors is usually(!) no cause for concern.

If the pending sector count keeps climbing, the drive is either slowly discovering the damage of a major adverse event or there's a major issue and failure is imminent.