Parity Valid - Last Checked Meaning

[Stupifier]

Was just looking for a quick help answer. I recently moved around 500 GB of data around between physical disks on my array and Cache Drive. Under my UnRaid Dashboard Tab, I see it says the following:

 

Parity is valid
Last checked on Tue 13 Mar 2018 02:51:54 AM EDT (eight days ago), finding 0 errors.
Duration: 15 hours, 54 minutes, 13 seconds. Average speed: 139.8 MB/sec

I just want to better understand what this means. I know I installed my Parity Drive and it did its first Parity Check/Write on March 13. But I recently moved many files around......is Parity calculated on the Fly and are these most recent changes "protected" by my Parity disk still?

 

I was under the assumption the Parity Disk writes updates on the fly as files are written to/from individual physical array disks. I also thought Parity Disk Check was only necessary when initializing Parity Disk or When data is thought to be compromised. Just want confirmation or clarity on this.

Thank you!

[Wody]

Yes, Parity is calculated on the fly during writing, that is why you'll see the parity drive also having at least as many writes as the disks.

The verification is to make sure make sure it is still valid, and it will read all the disks, calculate the parity and compare it with the information on the parity-drive(s).

It is usually recommended to do this at least once a month or so, just to make sure, and with recent unRAID you can set up a schedule for that so you don't have to remember to do it.

Parity can go bad for example when the system is shut down unexpectedly, and something was written to a data drive, but not to the parity, and verification will check that. Or, a drive may be failing and have said something was written, but not actually done so.

 

 

[Stupifier]

 Thank you very much. very Helpful