Parity Upgrade and Data Drive Addition (from Old Parity Disk)


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Hi everyone,

 

I know this question has been asked a million times before, but given the risk to data, I would appreciate a review of my planned parity upgrade procedure. Thanks in advance!

 

Goal: Upgrade parity disk from 8TB to 10TB. Add old parity disk to data array.

 

Procedure:

 

1. Preclear the new drive. While the new drive is preclearing, also run a parity check.

2. Turn off array auto start.

3. Stop the array.

4. Remove old parity drive and insert new 10TB drive in that slot.

5. Select new drive for parity drive.

6. Start array with rebuild box checked.

7. After parity rebuilt, plug in old parity drive. Assign old parity drive to data array.

 

Questions:

1. Is this procedure correct?

 

2. Now, if I do this, what happens to the data on the old parity drive? How do I clear it (or does it get cleared automatically by virtue of being added to the data array)?

 

3. During the rebuild (with the steps above), the array should be available, correct?

 

I prefer this method to the parity swap procedure because I'm trying to minimize array downtime.

 

Thanks again for your help,

Torquewrench

Edited by T0rqueWr3nch
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Minor semantics aside, the procedure will work. I'm not sure where you got the idea of a "rebuild box" to check.

 

However, you can simplify it a little if you wish. When you are at the point of building parity with the new drive, instead of removing the old parity, you can set a new config with the option to keep all, then on the main GUI page change the parity slot to the new drive, and put the old parity drive into the desired data slot.

 

New parity will be built with all included drives, and when parity has been checked successfully you can simply select the option to format the old parity drive. No need to keep it out of the parity build and force it to be cleared and added later.

 

Also, there is no technical need for the new parity drive to be clear, so running preclear is purely for testing. It's still a good idea, but serves no other purpose than confidence that the drive is fit for use.

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I just meant the rebuild parity check box that appears when you are about to start the array.

 

4 hours ago, jonathanm said:

you can set a new config with the option to keep all

I am not familiar with that config- is that a specific configuration setting or are you just saying that I don't have to go through the steps of physically removing the hard drive and waiting for parity to rebuild? If it's the latter, then can I amend the above steps to:

 

1. Preclear the new drive. While the new drive is preclearing, also run a parity check.

2. Turn off array auto start.

3. Stop the array.

4. Reassign the parity configuration to the new 10TB drive.

5. Assign old parity drive as a data drive.

6. Start array with rebuild box checked.

7. After parity rebuild, there's apparently an option to reformat the "new" data drive? Do I need to stop the array for this?

 

Is that correct? Can the array still be up during this revised process?

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6 hours ago, T0rqueWr3nch said:

I am not familiar with that config

3b. Tools - New Config - Preserve current assignments - All

 

6. Start array.

 

Array will be online during the parity build, you don't need to stop the array to format the former parity data drive.

 

If more than one drive shows "unmountable", don't do the format step.

 

Post screenshots and ask for help if any part of the process doesn't look right to you, or you need clarification.

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On 7/17/2019 at 6:19 AM, jonathanm said:

3b. Tools - New Config - Preserve current assignments - All

 

6. Start array.

 

Array will be online during the parity build, you don't need to stop the array to format the former parity data drive.

 

If more than one drive shows "unmountable", don't do the format step.

 

Post screenshots and ask for help if any part of the process doesn't look right to you, or you need clarification.

Just kicked off the parity rebuild!

 

I went to new config and preserved the cache and data slots since I was upgrading the parity drive. After that, I made sure my new 10TB drive was selected as the parity drive and added my old parity drive to the data array. I then started the array. 

 

My old parity drive was not originally available in the array since it was listed as "Unmountable: No file system". I then remembered I had to format it so I scrolled to the bottom and clicked the "Format" button. After a few minutes, the parity drive appeared as available in the data array.

 

Question: Was it okay to go ahead and format the old parity drive in the data array while I was rebuilding parity with the new drive? I ask because it seems to be out of line with this procedure: 

Will formatting my old parity drive in the data array harm the data on my other drives or the parity calculation? Or is the suggestion in the linked procedure just so you have a "backup" parity drive in case the new parity rebuild fails?

 

The reason this also bothers me is this claim that unRAID clears the disk prior to allowing it to be formatted so the new disk doesn't affect parity:

 

If this is the case (and it does appear so- the disk looks blank from the GUI navigator), how is unRAID able to do it so quickly when the preclear takes days?

 

Like I said, I think everything went well, these are just questions I had. Thanks again for the help and putting my mind at ease!

 

 

 

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21 minutes ago, T0rqueWr3nch said:

Question: Was it okay to go ahead and format the old parity drive in the data array while I was rebuilding parity with the new drive? I ask because it seems to be out of line with this procedure: 

It was OK to do this.  A format is just a form of write operation and the parity build process can handle writes occurring to the array while it is running.  Such writes will slow down the parity rebuild process (and the write operation) but in the case of a format this would only be by a matter of minutes but larger writes have more impact.  There is also the fact that if a data drive fails while building the initial parity the contents  of the write could be lost.

 

33 minutes ago, T0rqueWr3nch said:

Will formatting my old parity drive in the data array harm the data on my other drives or the parity calculation? Or is the suggestion in the linked procedure just so you have a "backup" parity drive in case the new parity rebuild fails?

No harm is done.   The reason is all about failure of a data drive while attempting to build the new parity.   If the following conditions are met:

  • The old parity drive is kept intact.
  • No data is written to the array while attempting to build parity on the new drive.

then these is a process (albeit a little tricky) where the old parity drive can be used in conjunction with the 'good' data drives to rebuild the data on the failed data drive.   It is basically a risk/elapsed time trade-off and the recommended process minimizes risk at the cost of increasing elapsed time.

41 minutes ago, T0rqueWr3nch said:

The reason this also bothers me is this claim that unRAID clears the disk prior to allowing it to be formatted so the new disk doesn't affect parity:

This is only done if you already have parity fully built.  It is not required if you are in the process of building initial parity (or have no parity disk).

 

50 minutes ago, T0rqueWr3nch said:

If this is the case (and it does appear so- the disk looks blank from the GUI navigator), how is unRAID able to do it so quickly when the preclear takes days?

This is because you were running the parity build process.  In such a case whatever is already on the disk is automatically included in the parity calculations so it is not a requirement that the disk contain only zeroes. 

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