Hey Unraid!

 

Loving this OS atm. Using it for a few months now. Having panic mode on at the moment.

Long story short: Wanted to migrate HDD's (3 disks, 2x 3TB and 1x 6TB) to a new server. When i unplugged the 6TB power cable, apparently something broke off. (The plastic underneath the golden connector pins of the SATA power port). It is my parity drive so i went a bit into panic mode. The plastic was somehow still a bit stuck in the PSU of the old server. So, i carefully placed the power connector back, thinking i will migrate later and hopefully get it back to work again.

It worked. So now my server is still on the old hardware, afraid to unplug the power SATA as i probably cannot replug it anymore. I mailed the web shop, they want me to send it in for replacement. Now i have a few questions:

 

Can i just shut down my server, unplug the parity drive. Wait for replacement and reboot the server with a replacement once it arrives and expect everything to work as normal? Or do i need to do some magic here? I can not place both drives in there and first sync parity on the new one of course. Or place back the old one if it fails.

The array probably wont start without a parity drive huh? So, i wont be able to access my data for the time being?

But is it safe to do this? Please, help me get my mind at ease. 

 

Thank you for the replies.

Edited November 5, 20196 yr by Dikkehein

No need to panic. Parity doesn't contain any data. It only has bits that allow the data for a missing disk to be calculated from those parity bits PLUS the bits on all the remaining disks.

 

You can definitely start the array and access its data with parity missing. In fact, if it was a data disk that was missing and parity was OK, you could even access the data on the missing data disk, from that same parity calculation I mentioned.

 

What you can't do with a missing disk is have any redundancy in the event of another disk failing in some way.

 

When you get the replacement disk, you would just install it, assign it to the slot of the disk you are replacing (parity in this case), and Unraid will rebuild the disk contents using that same parity calculation I mentioned.

 

 

Understanding parity can help make sense of many things about how Unraid manages your disks.

 

Here is the wiki on how parity works:

 

https://wiki.unraid.net/UnRAID_6/Overview#Parity-Protected_Array

Great! Thank you! So i can easily replace the parity disk. Good to know. Thank you very much. I will read the parity page also. 

IF you are really paranoid, leave the old parity disk in the PC.  When you get the replacement drive assign it as Parity 2 and start the array.  Unraid will now generate the required parity information and write it to the new disk.   You can then remove the old parity disk at your convenience and you will have had (at least) single parity protection during the entire replacement process. 

 

Note of Disclosure:  Parity 1 is a very simple calculation using an instruction that has been a part of the basic command set since the days of the Intel 4004 CPU.  Parity 2 is a complex matrix operation that usually takes a lot of CPU cycles to complete.  Depending on your CPU, your parity checks may take longer to complete.  With a modern mid-range CPU (post 2015), you probably won't see a difference.

Edited November 5, 20196 yr by Frank1940

13 minutes ago, Frank1940 said:

IF you are really paranoid, leave the old parity disk in the PC.  When you get the replacement drive assign it as Parity 2 and start the array.  Unraid will now generate the required parity information and write it to the new disk.   You can then remove the old parity disk at your convenience and you will have had (at least) single parity protection during the entire replacement process. 

 

Note of Disclosure:  Parity 1 is a very simple calculation using an instruction that has been a part of the basic command set since the days of the Intel 4004 CPU.  Parity 2 is a complex matrix operation that usually takes a lot of CPU cycles to complete.  Depending on your CPU, your parity checks may take longer to complete.  With a modern mid-range CPU (post 2015), you probably won't see a difference.

Thing is, the webshop wants me to send in the HDD for "inspection and replacement". So dual parity is no option. But i guess i got it figured out. Hopefully. Thank you for the information though! Maybe it will help in the future.