I have two UnRaid servers that are several years old now.

5 disks plus 2 parity on one, and 7 disks plus 1 parity on the other.

At first I ran Parity-Checks every 30 to 60 days. More recently I seem to remember to do it at 120 or more day intervals. It takes in the neighborhood of 25 to 30 hours to run the parity-check on each system.

No errors ever found on either system.

Any input on how often to run parity checks?

You have asked a question to which there is no 'right' answer! Many of us run a parity check once a month. It is always our hoped-for- goal to find no errors. Once you have an error(s), you have a potential for a data loss. And you should address the problem at once. You also want to find problems before a second problem occurs. (Once, you have two source of errors on an array, the likelihood of a data loss just jumped astronomically.)

Here is link to an old thread that has a look at the problem from a statistical viewpoint. You can read the comments of forum members at that time. Most of the still apply!

https://forums.unraid.net/topic/50504-dual-or-single-parity-its-your-choice/

About the long time to run the parity check. Have a look at Parity Check Tuning plugin. It allows to break these long running operations up into chunks that can be run during more convenient hours.

Remember that this test is intended to catch problems at their beginning before they become major headaches.

PS---- I know that the annual failure rates that I used in the Tables is much higher than we see today! (Thanks for some blessings!!!) But there were a few drives back then that did have annual failure rates of 10%. Today, a drive that has annual failure rate of 2% is the outlier.

Edited July 17Jul 17 by Frank1940

I personally run one every other month except I skip july

Jan, March, May, Sept, Nov are the months I run mine

I run a parity check once a quarter (Jan, Apr, Jul, Oct). I used to do it monthly but found that the system was stable enough that it never produced errors. Since reducing the interval to quarterly a couple of years ago, only once have any errors been found and I am happy to run parity check at that interval.

Both systems on which I have parity have five array data drives and a single parity disk.

Edited July 17Jul 17 by Hoopster

Setup Notifications to alert you immediately by email or other agent as soon as a problem is detected.

After running it monthly for a year or so, I have set it to quarterly now since 3 yrs. No errors until now.

Having 2 parity drives in an array is too much I think. Disk failures today are luckily unfrequent statistically so having one fallback drive is usually enough. Maybe if you have 20+ drives in your array, 2 parity drives would be a good idea though still not needed.