Searching through the forum I can see that this issue has been discussed quite a bit, but some of the work arounds seem a little far fetched.

 

I found one thread that stated that since parity checks only take about 5 or 6 hours I should just start it right before bed. It was an older thread and parity check speeds must have been a lot faster then. My checks typically take about 23 hours so this isn’t really a good work around.

 

Found another thread that stated that a parity check was only needed after an unclean shutdown, so it really isn’t a problem, all I need to do is disable scheduled parity checks. Really. If scheduled parity checks aren’t needed I have to wonder why the ability to run them is included in the system, and enabled by default IIRC. Would really appreciate any confirmation/denial of this.

 

Any other ideas how I can keep the parity checks from hogging my system or perhaps minimize their impact via scheduling (currently using monthly).

2 hours ago, wgstarks said:

If scheduled parity checks aren’t needed I have to wonder why the ability to run them is included in the system, and enabled by default IIRC.

Need is maybe too strong of a word, but they sure are prudent. Not only for the detection of parity inconsistency, but mostly for the regular exercise of disks. If a disk is purely archive, it may never be called upon to read, but if another drive fails, the long dormant drive will suddenly be called into duty to perform perfectly in the reconstruction of the failed disk.

 

Think of regular parity checks as confirmation that the system is healthy and able to perform a recovery if a drive fails.

 

Traditional RAID systems that stripe data across all volumes don't have to contend with this exact scenario, as all drives are spun up and read from every time the system is accessed. Unraid is pretty unique in the ability to keep certain drives spun down during normal usage. Problem is, if the drive is never used, it can fail silently and bite you when you need it most. Regular parity checks keep an eye on your drive health.

I can see that. Are monthly checks really necessary though? Maybe 3 or 4 times a year? Or maybe it would be better to just stop the check when necessary for performance and start it over the next day?

17 minutes ago, wgstarks said:

Are monthly checks really necessary though? Maybe 3 or 4 times a year?

It all depends on your risk tolerance. The next closest thing to a parity check would be long smart tests, those you can start on individual disks whenever you feel like it, and they should only be run when that specific drive is expected to be not needed for the duration of the test to ensure a clean run. It shouldn't affect other drives performance.

 

A parity check is needed after unclean shutdown though.

 

4 hours ago, wgstarks said:

It was an older thread and parity check speeds must have been a lot faster then.

No, it's more that drive throughput in MB/s has not increased linearly with capacity. One of my test servers takes around 4 hours for a parity check, because it only has 1.5TB drives and still manages 90+MB/s, where my main production server takes 19 hours because it has 8TB parity and only manages 115MB/s. It would be much quicker if ALL the drives were 8TB instead of only a few.