High Loop2 Reads


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I’m having a new issue where my Loop2 process is reading insane amounts of data (350-400MB/s) from my cache (2x 500GB WD Blue SSDs in BTRFS RAID1) when I’m watching 4K videos in Plex Docker.  The bursts last for 5-10 mins or so.  I know it’s Loop2 because it’s showing in IOTOP s the top process when it’s happening, and the read rate matches the Unraid interface.  In this case, the Plex movies are on the cache, and my docker and all system/domains files are on cache.  I have an E5-2699v4 CPU (42 threads) with 50% dedicated to Plex.  All Plex metadata is on the cache as well.  


Now, I’m direct playing the videos in Plex Docker, so I’m not transcoding there.  I don’t know that it’s related to the 4K movies playing, but that’s when I notice it (it eventually chokes the docker service and Plex stops for everyone watching).


So, to trouble this from the Unraid perspective, how can I see into the Loop2 process to understand what those reads really are? 


EDIT:  This doesn’t happen constantly, only in these bursts, which is why I’m not yet sure that it’s related to the Plex activity. 



Edited by Andiroo2
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  • 4 weeks later...
  • 3 weeks later...

I'm having the same issue as well.  Was researching and posted to the below linked topic.  I'm going to remove that docker and try a different Plex Docker Image.

I add the repository which I think is directly from plex (https://github.com/plexinc/pms-docker).


I originally thought it was a brtfs issue with the cache but it doesn't seem to be the problem... ?


Any solutions on your end?







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I'm pretty certain Plex isn't the cause in my issue linked above. I re-created my docker.img btrfs with no effect.


/dev/loop2 is the docker image that lives on the cache drive (usually). So it's not just used for Plex - but for any/all dockers you may have running.


Note that the issue we are seeing is lots of *reads* (this thread and mine linked above), not writes on the /dev/loop2 device.

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  • 2 months later...

I'm seeing the same behaviour, docker loop device is showing a very high amount of reads. System load climbs to ridiculous amount, CPU usage shows as 100%, server becomes unresponsive/sluggish/things start crashing/misbehaving.

I've moved 'docker.img' to a separate SSD from 'app_data', but that hasn't helped.

Does anyone have a resolution?

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My original issue was related to Plex RAM transcoding set up incorrectly. I was transcoding to /tmp, which allowed the Plex docker to eventually use all the available RAM in the system without properly freeing it up when it ran out. 

I changed to a fixed RAM disk instead, set to 12GB, and the system has worked perfectly ever since. When it approaches 12GB used for transcoding, it properly frees up RAM on the RAM disk and transcoding keeps on moving without impacting the rest of the server. 

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15 hours ago, soabwahott said:


I am still running 6.8.3 and have this issue, so I don't think this is related to 6.9.x.


I do run Plex but it's not a transcoding issue. 


Are you running Crashplan? I don't believe Crashplan is specifically the problem, but perhaps somehow causes it more often. At the moment my system is doing it within a few hours of starting the Crashplan docker.

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