When my server is doing a parity check, the connection slows down so much that it is hard or impossible to watch recorded TV that is stored on the server. I don't have anything running on the server or other than TV being taken on/off the server.

I had to buy a new home theater computer, which is what I use to watch recorded TV. So, it's about as fast as it can get.

Right now, the server is doing a parity check and the CPU load is only around 2%. What could be the cause of the slowdown?

CPU it's not typically the problem; all disks are being read at their max speed. Try scheduling the parity check overnight.

Thanks. The parity check usually goes over night, but goes 16 hours or so. If it starts at midnight on the 1st of the month (which is how I think it's set, but I'll look), it lasts until 4pm the next day.

Yesterday, I replaced the parity drive because it had thrown an error a while back and people here said I should do that. So, it ran from the afternoon yesterday, and it's sill going this morning. And, we have plenty of times when we get power outages, where the system doesn't shut down correctly (don't know why -- most times, it does not, but sometimes it does; like yesterday it did a clean shutdown, but last week did not). I have a battery backup, but there's no power, so I can't interface with the server. (I can after I get a gas generator going, but that takes a while.) I have the system set to begin shutdown not too long after power goes out, because the backup has to run WiFi, and I want that on as long as I can. Once we get power back, the system automatically starts a parity check if there was no clean shutdown.

Is there no way to prioritize this, so that the parity check has lower priority than fetching data or is stopped while fetching data? Or is the solution to go from spinning disks to all SSDs?

You can try playing around with some disk setting tunables, mostly md_queue_limit and md_sync_limit

You can also use the Parity Check Tuning plugin to get even more control.

4 minutes ago, itimpi said:

Parity Check Tuning plugin

Right, you can run it in increments during the night only, I believe even stock now supports that, forgot about it.

Thank you. The parity check took 15 hours and 40 minutes for the parity check, which I seem to remember is normal.

I am going to upgrade from version 6.9.2 to version 7.x.x. I was trying to fix the cache drive issue before I did that. Then, I'll look into the parity check tuning plugin.