I just noticed that one of my older 2TB drives has a reallocated_sector_ct=192.  Now I know that this means that it has remapped this many sectors and that the drive is still functioning.  What I don't know is if this is considered a high number for this size of drive.  I mean, if there are thousands of redundant sectors, then 132 would be low, right?  Should we be worried about this number?

 

 

I just noticed that one of my older 2TB drives has a reallocated_sector_ct=192.  Now I know that this means that it has remapped this many sectors and that the drive is still functioning.  What I don't know is if this is considered a high number for this size of drive.  I mean, if there are thousands of redundant sectors, then 132 would be low, right?  Should we be worried about this number?

Depends.  There are a few users here which immediately replace drives once they start showing any reallocated sectors.  Most of my drives have 0 reallocated, a couple have a single one, and one of them shows 368.  The one with 368 has shown that many for as long as I can remember.  I do watch it like a hawk however, and if it ever does begin to increase again I will be removing it from the system.

 

If however, smartctl shows that its Failing Now on that attribute it means that the drive has exhausted its pool of spare sectors and now its time to immediately replace it.  But like you said, that pool size is usually at least 1000.  (Only have ever had a single drive in my life that ever hit that stage)

Keep a careful eye on it and see if you have any Pending Reallocated Sectors. They can invalidate and corrupt your parity and data.

The reallocated sectors are more a symptom of a failing drive than a death sentence themselves.

 

As Squid remarks, with 368 reallocations that hold steady parity check after parity check, the drive is probably fine. The disk has reallocated the bad sectors and if those sectors are not accessed again, in theory the rest of the drive is fine.

 

But the problem is, in a very large percentage of cases (very close to 100%), even a single reallocated sector is the beginning of the end for the drive. Seems every parity check causes the number to increase a little. Before you know it, 1 has turned into 34, and then 182, , and you know that the disk is toast. I refer to it as the pothole effect - a small pothole just keeps getting bigger and bigger until it is fixed properly. Unfortunately fixing a disk properly means replacing it.

 

I have a simple test. If a reallocated sector shows up, run parity checks ever day or two for a week. If you can get 3 parity checks in a row with the reallocations not growing, the disk is safe (although you should continue to monitor it for more problems). But after 4 or 5 parity checks you haven't gotten 3 good ones in a row, the disk is going south.