Add a Cleared Flag without clearing or Pre-clearing


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2 minutes ago, DoeBoye said:

Hi,

Is there a way to manually add the 'Cleared Flag' to a disk so unRaid just formats it and adds it to the array when I assign it to an empty slot?

No.

 

Why would you want to do that anyway?   Doing it the way you describe would invalidate parity so that you would be unprotected until you rebuilt parity.

 

Note that if you do not have parity you can already add a disk without first clearing it.

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hmm... perhaps I'm not entirely clear on how it works, but why would parity be invalidated by adding a new disk to the array in a previously empty slot that just hasn't been pre-cleared? I assumed once unRaid formats it and adds it to the array, all will be good...

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11 minutes ago, DoeBoye said:

hmm... perhaps I'm not entirely clear on how it works, but why would parity be invalidated by adding a new disk to the array in a previously empty slot that just hasn't been pre-cleared? I assumed once unRaid formats it and adds it to the array, all will be good...

For parity to remain valid every sector on the added disk needs to contain zeroes.    If this is not the case then parity does not remain valid when adding the disk.  Parity can only be made valid by doing a parity build that reads every sector off every disk as part of the parity rebuild process.   That is why the normal process of adding a disk (that is not already pre-cleared) initiates a 'clear' phase to write zeroes to every sector on the disk being added before it actually makes it ready for use

 

reading up on how parity works in the online documentation might help you understand this better.

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  • 2 weeks later...

Thanks itimpi! I guess I hadn't thought my question through entirely before posting. I've been working through some data loss issues and was getting irritated when drives I knew were good needed to be pre-cleared again to add to my array. I was looking for a shorcut :)

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1 hour ago, DoeBoye said:

Thanks itimpi! I guess I hadn't thought my question through entirely before posting. I've been working through some data loss issues and was getting irritated when drives I knew were good needed to be pre-cleared again to add to my array. I was looking for a shorcut :)

Not sure if what you mean by "add" is the same as what unRAID means or not.

 

Adding a drive to the parity array means adding it to a new slot. When adding to a new slot, a drive must be clear so parity will remain valid, since a clear drive (all zeros) has no effect on parity.

 

If you are using a drive to replace and rebuild another data drive, or to replace and rebuild parity, or to rebuild to the same slot it was in, it is not necessary for the drive to be clear since it will be completely overwritten based on the parity calculation and so will not invalidate parity since its new contents will be based on parity.

 

You should assume a brand new drive has random data on it. Sometimes a new drive (especially if "shucked" from an enclosure) will be preformatted to NTFS. But an empty NTFS filesystem is not clear, since the filesystem itself is data.

 

If there is no parity drive, or if you intend to set a new config and rebuild parity anyway, it doesn't matter whether any of the data disks are clear or not.

 

People often preclear a new drive even when they don't need a clear drive because preclear is one way to test a new drive.

 

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All true!

This is a case of frustration + over tired = irritated, poorly thought out post.

Please do not waste any more bandwidth on it! :$

 

[EDIT] Frankly, I'd say "mods, please delete, it's a waste of a database row", but it does have some useful info re: parity checks and such :)

Edited by DoeBoye
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