I have always thought that upon buying a new drive for one of my unRAID servers it would be prudent to do at least one preclear run on the drive. Lately however, I have noticed some people suggesting it's not really necessary as the 'workout' the drive gets upon being put into an unRAID server is almost as good as doing a preclear anyway.

 

Thoughts? 

 

I am going to be swapping out some 8TB parity drives with 10TB drives in a few of my servers soon, just wondering if I should do preclears on them?

 

I know it comes down to personal preference, but does the 'workout' a drive gets when newly added to an unRAID server come close to what a preclear accomplishes?

I think not, and will continue to preclear. Just one pass is enough for me, because a failure is, after all, recoverable.

 

The way SMART works in the drives is this - if a sector is attempted to be read, and has a problem reading that sector, it will mark the sector as pending. When it is then written, SMART has the opportunity to confirm the bad sector and reallocate it. And then when it is read again it can be confirmed that it is valid or made pending again. Preclear mimics these three stages, and really does an excellent job of detecting issues and allowing SMART to do its job. Adding to the array just clears it (no reads), until the ensuing parity check. And would leave you doubting the disk for some time until it has past some threshold of trust.

 

I personally prefer the confidence of adding a drive only after it has been precleared successfully. I then don't have to deal with early drive failure, rebuilding disks, etc. And am confident that the drive is sound.

 

Interestingly I've had the most problems with drives that were not precleared (I've only had a few in my unRAID users, and it was long ago). Call it coincidence, but I believe there is some "therapeutic" value of giving the drive a gentle break in with relatively low stress sequential activity for its first few days of life.