Is it necessary to pre-clear drives?

[DigitalRobot]

Hi there,

 

I've read a bit about pre-clearing drives before using them in the array, I want to make sure the drive doesn't have manufacturing defects and be confident it won't die in its first month. What I'm trying to do is replace an existing 1TB drive with a 3TB drive. I read somewhere that you only need to pre-clear if you're adding and don't need to pre-clear if you're replacing.

 

Do I need to pre-clear my new drive? If so, how do I go about doing that?

 

Thanks in advance,

 

DigitalRobot

[JonathanM]

1 hour ago, DigitalRobot said:

I want to make sure the drive doesn't have manufacturing defects and be confident it won't die in its first month.

Preclear is only 1 of many different ways to accomplish this goal, so no you don't need to preclear.

 

The drive manufacturer has tests, as well as the built in SMART extended tests, and there are other third party utilities available. What is best and easiest depends on the other PC hardware you have available to you.

[trurl]

1 hour ago, DigitalRobot said:

I read somewhere that you only need to pre-clear if you're adding and don't need to pre-clear if you're replacing.

Unraid only requires a clear disk when you are adding it to a new slot in an array that already has valid parity. This is so parity will remain valid. A clear disk is all zeros, and all those zeros have no effect on the parity result.

 

If you don't preclear a disk when adding it to a new slot in an array with valid parity, then Unraid will clear it for you. So, preclear is never necessary.

 

Much older versions of Unraid would take the array offline when clearing a disk, so preclear was created to clear the disk before (pre) adding it to a new slot.

 

People still use preclear to test and "burn-in" a disk. If you want to test a replacement disk then you can use preclear for that, but a clear disk is not required for a replacement disk.

[Squid]

1 hour ago, DigitalRobot said:

I read somewhere that you only need to pre-clear if you're adding and don't need to pre-clear if you're replacing.

Depends upon your point of view.  (And personally, I have never bothered to preclear any drive once it basically was no longer strictly necessary to do it)

 

A rebuild / replacement of an existing drive will wind up writing to every sector of the drive, and you can look at if there were any reallocated / pending sectors after that happened and make a decision for yourself.  If you follow that process by then running a parity check, effectively you've done everything a preclear does (single pass) and a rebuild in 2/3 the time.

 

But, some people won't trust a drive unless it does a few passes of preclear.  It's really up to your own comfort / paranoia level.  Just because a drive was never precleared doesn't mean it will fail within the first month.  Just because a drive was precleared with many passes also doesn't mean that it won't fail within the first month.  Myself I have never had any hard drive throughout my existence ever fail within the first month, and have only had a 1-2 actually fail within warranty, and I've probably purchased ~200 drives in my life for personal use.

[trurl]

And, to continue with Squid's point, even if you do have a drive failure, you should be able to recover from it. That is the whole point of parity, after all.

 

And you should always be sure you have another copy of anything important and irreplaceable. Parity is not a substitute for backups, and if you have a good backup plan, you should be able to worry less about a new disk having "infant mortality".

[DigitalRobot]

Thanks for the wisdom everyone! Given that the drive I'm replacing is functional (and so if worst came to worst the data would still be on it) and that the array is parity protected and in good health my level of paranoia is really low.

 

Much appreciated!