Tool - New config - "preserve Array" does not select "Parity is valid"

[DataCollector]

Hello.

 

I made a change on one of my Pools (unplugged 3 small NVMe SSD and stuffed a big NVMe SSD in my System).
Since unraid remembered the old 3 SSDs I had t o use the Tool "new config".

I selected to preserve my Array and applied the change.

 

here it comes: Why does unraid tell me the parity will be overwritten?
The Array is okay and i did select to preserve the Array (all of it).

 

Since I was to hasty I saw later (to late) the option to select "parity is valid".

I would have guessed when I want to select to preserve/keep my Array that option would be "on" by default. But no.

Now I will have to wait around 1 day since the Parity is build anew.

 

Just my 2 cents: but I think, it would be better to switch the "parity is valid" on, when someone selcts to keep its array with the Tool.

 

[JorgeB]

3 minutes ago, DataCollector said:

to select "parity is valid"

You need to check this in addition to preserve the array, preserve the array just keeps all the assignments.

[itimpi]

I think defaulting to off is correct.   Normally when one uses that option you are going to make a change to the drive assignments that will invalidate parity.   If it was set on by default users would not change it and automatically assume their parity (despite them making a dtive change) was valid and only finding out later after a drive failure it was not so data recovery is impossible.

[trurl]

If you did make assignment changes in the array, parity is NOT valid and has to be rebuilt.

 

I guess you were must making assignment changes to pools

[DataCollector]

2 hours ago, itimpi said:

Normally when one uses that option you are going to make a change to the drive assignments that will invalidate parity.

 

Why should changing the Drive assignment inside the Array mage the Paritydata invalid (at least, when only 1 Paritydisk is in use)?

If the Disk is in Place 1 oder in place 6 does not change the bit-value. And as far as I read and saw in the explainations: the Parity (only 1 Paritydisk) just contains the bitvalue of all the disks in the array.  1 or 0. that does nit change, if the position in the Array is changed.

 

And why should someone chose "preserve Array" when the target ist not to preserve the Array?

 

2 hours ago, itimpi said:

If it was set on by default users would not change it and automatically assume their parity (despite them making a dtive change) was valid and only finding out later after a drive failure it was not so data recovery is impossible.

 

If I chose to preserve the pool or nothing, then the user wants to change the Array and then the parity may be invalid.

But if you select "preserve array" then you dont want to change the array. So the parity ist in the same stage it was before.

That does nit make the parityinformation invalid.

[DataCollector]

2 hours ago, trurl said:

If you did make assignment changes in the array, parity is NOT valid and has to be rebuilt.

 

I guess you were must making assignment changes to pools

Like I explained: I chose "preserve Array" because I dit change absolutely nothing on the array.

 

I just changed one of my 2 pools from "3x NVMe SSD 2TB zfs raid5"   to     "1x NVMe SSD 4TB xfs".

The Array was untuched.

[JorgeB]

57 minutes ago, DataCollector said:

I chose "preserve Array" because I dit change absolutely nothing on the array.

You just then need to check "parity is already valid" before array start.

 

You could for example have a disabled disk before the new config, preserve the array would preserve all except that disk, and parity would no longer be valid, requiring a parity sync, so it's up to the user to choose if it's valid or not after a new config.

[DataCollector]

1 hour ago, JorgeB said:

You just then need to check "parity is already valid" before array start.

 

Yes, now I know that... But why?

When want to preserve the array, I do not want to change anything so th eparity is valid and that the option "parity is valid" shpould be checked already.

When I want to change the Array I make a note (screenshot) which Disk is at what place and do not preserve the Array in the tool then the option "parity is valid" shpuld be unchecked.

 

1 hour ago, JorgeB said:

You could for example have a disabled disk before the new config,

Then I want to change the array.

 

1 hour ago, JorgeB said:

preserve the array would preserve all except that disk, and parity would no longer be valid,

 

If I want to replace a disabled disk I want to let unraid recreate that replaced disk. So that depends on validity of the parity.

 

[JorgeB]

7 minutes ago, DataCollector said:

Then I want to change the array.

Not necessarily, frequently users get a disabled disk, and they don't have a spare to install, or don't want to buy a new disk now, so they move the data to the other disks, and do a new config without it, they can still preserve the array assignments, but parity won't be valid.

[trurl]

Safer to default to rebuild parity. Unraid doesn't know why you did New Config, and New Config can be used in ways that invalidate parity. If the user knows why their parity would be valid after New Config, then they can know to check the box. There certainly have been users who incorrectly thought their parity would be valid after they did New Config even though they used it in a way that invalidated parity.