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Drive replacements & data loss

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Unraid  6.5.2

I’m not sure if the data loss is caused by mine own actions or this is software bug. I was replacing drives in my server. I purchased two 12TB drives. One would replace parity drive, and second would replace one of array drives. I precleared both drives. The total array size was 15TB with only 200 GB free space left. These are the steps that I took:

1.      Replaced parity drive

2.      Rebuild parity

3.      Replaced smaller drive with 12TB drive

4.      Started array

The process of rebuilding drive has started, but I realized that I forgot to format drive as XFS. By default, it was set to reiserfs.

5.      I cancelled rebuild process & changed drive format settings to XFS

6.      Unraid informed me that drive needs to be formatted

7.      After formatting drive, the process of rebuilding of array has started again

Rebuild was completed and I decided to replace another smaller drive with previous parity drive. This time I ensured that drive format setting was set to XFS. Once, unraid detected new settings, it formatted drive and proceeded with rebuilding array.


I noticed that something is off when I started docker again. All my apps were missing. Then I noticed that the array used space is now only 9.7TB. The difference is equal to two smaller drives that I removed. Bear in mind that during second drive replacement I did not interrupt the process at all.

Luckily, I still have two smaller drives intact. I’m copying the files from them back to new 12TB disk (disk to disk)  


I'm little bit reluctant to do another drive replacement in the future. As I said this could be caused by mine own actions, but cancelling rebuild process should not have such an effect. Before I proceeded made sure that parity is valid. 

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Thanks. I know this procedure, however when you are replacing with new drive and you want to set new file format, unraid will perform formatting anyway. We are not performing conversion from RFS to XFS. Parity has no specific file format. Based on what you have said, part of parity that relates to swapped drive will be deleted. To tell the truth I do not know how is this possible without recalculating parity. Most of the users will not know this. They would simply swap drives and set desired file system in the process. They would definitely not know that their array could be affected, despite the warning message that appears next to new drive.  

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1 minute ago, talkto_menow said:

however when you are replacing with new drive and you want to set new file format, unraid will perform formatting anyway. 

Like I already said, and it's also the first question on thread in the link above, you can't change filesystem and then rebuild from parity, parity rebuilds the disk bit by bit, including whatever filesystem it was originally, you should read this to learn how parity works, it should make this issue pretty clear.






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