I have just built a new server with an 8TB parity drive, and data drives of: 1x8TB, 2x4TB.  A parity check in this system seems to take from 18-24hrs.  I have an old system with a 4TB drive and parity checks on that system take about 12 hours so around 24 hours seems reasonable.

 

But while the parity check is running I experience significantly degraded performance.  Here is one example - when I use SageTV to play back video files the playback can be herky jerky at times.  When I try to skip forward over commercials it takes the system several seconds to catch back up.  If I pause the parity check then these problems completely go away.

 

Is that expected performance?  Or do I have something wrong on my system?

Most people use the Parity Check Tuning plugin so that the scheduled checks run in batches during off hours (ie: mine run between midnight (when I go to sleep) and 4 am (when the wife gets up) and resumes the next day until its completed).  But, yes since there's competing bandwidth depending upon how much bandwidth is required by the media, pauses etc may result

15 minutes ago, wayner said:

A parity check in this system seems to take from 18-24hrs

My system with 4 8TB + 8TB parity takes ~ 16.5 hours on a consistent basis.  The 4TB drives will likely slow it down a bit as higher density drives go a bit quicker in a parity check.

 

My monthly parity check started at 1am today and is 60% done when the Parity Check Tuning plugin paused it to resume again at midnight.  I do not notice slowdowns in other things during a parity check because I schedule the check to run in chunks of downtime over night.  However, before using the Parity Check Tuning plugin, file access to the array could be slow at times.  I did not notice a ton of difference in Plex because content mostly direct plays and does not need a lot of processing, However, some slowdowns are inevitable as multiple processes compete for access to files and bandwidth.

 

Early this morning while the parity check was still running, I did notice that CrashPlan was also running a backup and Plex was doing a media scan.  Performance seemed normal as I accessed a few shares and navigated around in the GUI.

Edited January 15, 20224 yr by Hoopster

19 minutes ago, Squid said:

Most people use the Parity Check Tuning plugin so that the scheduled checks run in batches during off hours (ie: mine run between midnight (when I go to sleep) and 4 am (when the wife gets up) and resumes the next day until its completed).  But, yes since there's competing bandwidth depending upon how much bandwidth is required by the media, pauses etc may result

Thanks - I did not know that you can do it in batches but that should solve the issue.

One further question on this - do you have to worry about conflicts with the CA backup plugin or are the plugins smart enough to not run at the same time, and/or does it not matter if they are running at the same time.

Doesn't matter.  Backup would just be slower.  

3 minutes ago, wayner said:

One further question on this - do you have to worry about conflicts with the CA backup plugin or are the plugins smart enough to not run at the same time, and/or does it not matter if they are running at the same time.

The Parity check Tuning plug-in does not take account of other plugins running at the same time.    There is a level of reduced performance in the parity check speed while the backup is running, but probably not enough to really matter.

It also looks like the Parity Check Tuning Plugin replaces the scheduler Plugin (or the core unRAID Scheduler function - I can't remember if I had to install this separately) as when I go to Settings - Scheduler I see the Parity Check Tuning Plugin.  Is that correct?

Yes.  They work in conjunction with each other.  Scheduler - Parity Check tells the system when to start it (eg: Monthly)   Parity check tuner tells the system when to pause it and when to resume (ie: next day at whatever time you want and for what duration...)

4 minutes ago, wayner said:

It also looks like the Parity Check Tuning Plugin replaces the scheduler Plugin

It is in addition to unRAID core Parity check scheduling.  You still set the schedule for parity checks through the unRAID core functionality and fine tune the increments through the Parity Check Tuning plugin.  Here is my configuration for once a month on the 15th with it running from 1:00 am to 9:30 am, pausing and resuming again at 12:15am.  It finished for me on that second increment before I start my day on the 16th.