Just precleared this disk as my new parity drive.

 

Preclearing 1 cycle took a total of 47 hours on my system. I used to do 3 preclear cycles but from now on I will keep it with 1 preclear cycle and possible 1 or 2 extra write cycles to save on time.

 

 0 sectors were pending re-allocation before the start of the preclear.
0 sectors were pending re-allocation after pre-read in cycle 1 of 1.
0 sectors were pending re-allocation after zero of disk in cycle 1 of 1.
0 sectors are pending re-allocation at the end of the preclear,
    the number of sectors pending re-allocation did not change.
0 sectors had been re-allocated before the start of the preclear.
0 sectors are re-allocated at the end of the preclear,
    the number of sectors re-allocated did not change.

 

I know it seems like forever, but I strongly urge you to continue your 3 cycle process. I have had several instances of the first cycle being fine, only to catch errors in the 3rd. You'll be creating a false sense of security imo, especially considering the density of the disk. All of my 4TB drives went through the same rigorous 3 cycle preclear that I used on the 3TB models. Instead of a 5 day preclear, it was 7. But I can feel confident that they are just as vetted as the smaller disks.

Ah, but why stop at three? Maybe a fourth or fifth just to be sure.

While it takes almost a week for them to preclear, I run 3 passes and will continue to do so.  I purchased both of my 4TB drives local.  I have 15 days to return them.  I would rather return the drive if there is any issue vs RMA them.

Ah, but why stop at three? Maybe a fourth or fifth just to be sure.

 

Three seems to be the point of diminishing return for preclear time versus failure rate. I could be wrong, but I also believe it is the minimum necessary number of cycles for a proper set of sample points for comparison.

 

Also, from this thread:

 

Basically what it comes down to for me is that while a first preclear may pass, it does not always find bad drives.  I had a couple of seagates fail on me after being in the array for about a month and after having passed a cycle of preclear.

 

From then on a do at least 2 and generally 3 cycles.

 

Subsequent cycles are an attempt to get past the early part of the "bathtub curve" where disks fail in their first few days of service.  Before they hold your data.

http://en.wikipedia.org/wiki/Bathtub_curve

 

Both of these are highly respected and experienced unRAID users, and Joe L. is the author of the preclear script. I'm sure some of the other venerable users on here concur. For something as critical as this, I like to trust the experts and am willing to sacrifice a little time for a lot more reliability.