Can someone point me in the direction and or maybe explain how performing a Parity Check while updating/writing data to the array works? I think I understand that a Parity Check is more or less a "verify process" more than a ""correct or fix process" where you might otherwise write new data to the array. When I'm reminded of Scheduled Parity Checks I tend to get paranoid about new data being randomly written to the array by misc docker containers and or guest vms etc... It seams like "Parity Corrections" are more or less "on the fly as detected" rather than during a Parity Check Process?

 

like, If a manual or scheduled Parity Check starts and somewhere about 35% or so parity check complete, I update and or write new data to the array, is the parity check effected at all? What if it checks a parity bit that I or a docker happen to be updating at the time? How does parity check now its valid or not other than being a 0 or 1 in the checking process?

 

How does Parity checking and or "writing corrections" work when performing a Parity Check?

 

Thanks for any info that can be provided!

 

~SOL

20 minutes ago, SomeoneOnLine said:

somewhere about 35% or so parity check complete, I update and or write new data to the array, is the parity check effected at all?

There should be no effect from data point of view. Parity needs to be valid at any point on every disk sector. The read write mechanism needs to be consistent and unraid guarantees that. You will be checking the state either before or after your ongoing writes, never an inbetween state. Same with writing corrections

 

You may still want to minimize array access during parity checks, because fast parity checks depend on sequential IO. If the drive heads have to move between parity read and data read often, that leads to very slow random IO. So there is a performance concern 

12 minutes ago, apandey said:

You will be checking the state either before or after your ongoing writes, never an inbetween state. Same with writing corrections

Thank you! That is what I was hoping and thinkg was the case. I was just looking to verify.