Unusable Read Speeds during Parity Check

[allischalmersman]

Hi guys.  I've been a long time UnRaid user.  Since like 2012 ish.  Only the last few months have I noticed that my server is pretty much unusable during parity checks.  I don't remember it being this way before.  Now I do have dual parity, and it is an 8TB parity check so it takes quite a while.  Over a day.  But when I say unusable I mean completely useless during parity check.  As in try to copy a large file and you get a few KB/s transfer speed.  Cancel the parity check and transfer speed instantly goes up to 112 MB/s.  CPU usage during parity check is like 50%.  Does this behavior sound normal?  

[itimpi]

It seems to vary according to your system specs.    The calculations for parity2 are much more CPU intensive than those for parity1 so those with older CPUs are more likely to notice a larger performance hit.  Having said that your system seems take a particularly high hit.  Even newer systems get a noticeable hit as an element of contention for the disks occur.

 

if you have upgraded to 6.7 then you might want to look at the Parity Check Tuning plugin that at least allows you to schedule the parity check to run in increments outside prime time (albeit at the expense of it taking a longer elapsed time to finally complete).