I've got a read error on my parity drive. So I changed it and started another parity check. Surprisingly the parity check speed is around 30-34MB/s, while the initial parity check was 100+ MB/s. I've gone through different topics on this forum looking for possible solution. Have tested hard drives using DiskSpeed, nothing abnormal there. All my drives are the same, wd purple 3TB and all of them have more or less the same speed during DiskSpeed test. Tried to disable Docker. No parity check speed change. Tried to perform parity check after rebooting in safe mode. Got parity check speed a bit higher, 34-38MB/s. What can cause such a parity check speed drop?

gen8-diagnostics-20221015-1244.zip

You are doing a parity sync, not a parity check, check the server BIOS for write cache, it's probably disabled, known issue with those servers.

I haven't changed any settings since the first parity sync, that was giving me 100+MB/s.

The question is why the parity sync speed is only 30% of what I had before.

6 minutes ago, JorgeB said:

check the server BIOS for write cache

 

Enabled it, but nothing has changed. Still getting 34MB/s parity sync speed.

Are you sure it's enabled? if it was disabled it should make a big difference.

Yes, bios setting shows it is enabled. But I am still getting exactly the same speed.

Find it strange that changing that setting didn't change anything, since 30MB/s is about the expected speed with it enabled, and it should give you 100MB/s+ with it disabled, post new diags in case there's something visible now.

It is strange indeed.

I re-installed unraid from the scratch, started parity sync and it shows 140+MB/s now. Really curious what could affect the performance so much.

That doesn't make much sense but glad it's solved.

We shall see how long it will last and if I will face the same issue again.