Is preclear enough?

[tucansam]

After reading some forum posts, I have settled on buying a couple of WD Green disks to finalize my build.

 

Over on newegg, many of the unfavorable reviews mention using WD's own disk utilities to test the drive (leading into high failure rates, but this is a separate issue akin to rolling dice).

 

I'm wondering if I should run WD's software on my new drives before I preclear... Or is preclearing each disk one (or two, or three?) times enough to establish a non-faulty disk prior to initialization in the array?

 

Thanks.

[Frank1940]

A hard disk can fail at any time.  However, if it works at all, it is most likely to fail in the first few hours after being put into service.  And after a couple of hundred hours of operation, the odds of any single drive failing are actually quite low.  That is, until the drive reaches its end-of-life--->20,000 hours.  Then the odds of it failing begin to rise.  It might fail at 20,002 hours or it might be 40,000 hours but all drives will eventually fail...

 

What these test programs do (Preclear in particular), is get you past that critical period when early drive failures are most likely to occur.  That way if a drive does fail, you don't have it in an array and have the problem of rebuilding an array.  The second thing many of these programs do is weed out those drives that have marginal reliability by writing data to the data to every byte on the drive and then checking to verify that the data can be read back from the drive.  If a drive passes all of these tests, it is not a DOA drive and it is past the early failure point for most drives.  At this point, the odds that the drive will fail in the next few months are very, very small.

 

You may ask why do some recommend more than one perclear cycle.  If the time for one preclear cycle gets the drive past 90% of the early drive failures, two cycles will probably get you by 95% of the early failures, three cycles might get past 99.9% of the early failures.  Statistically,  you can never get past the 100% point so there is a point of diminishing return to performing more and more cycles. 

[pantner]

From what i understand, a preclear will write over every sector of the disk and then read it back (i guess similar to memtest?) as well as other things.

 

This is a step beyond the WD tools as they are non-destructive tests, however it certainly won't hurt to do it.

 

You still want to do at-least 1 preclear as it will prevent UnRaid from doing its own check when adding it to the arrary.

 

I personally like to do 3 preclears.