Docker container using my boot drive even though I have my volume somewhere else

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I understand this may be something to do with docker and not your container but I’m scratching my head and fixing this. I have a system with a 2tb NVMe boot drive, which I also use for /var/lib/docker/volumes. I have a RAID6 array with 6-spinners and I bought one of those high-endurance NVMe’s to use for the cache (using bcache). My goal is to use this RAID array to backup my main server. After struggling with the linuxserver.io image and permissions I switched to the duplicati image and everything seems to be working as expected.

As I was running my first backup I noticed that my system drive (which at this time had my docker volume) was getting quite a bit of action, it appeared that everything getting written to my RAID drive was going through my system drive first. I do not want this as my system drive is a Samsung “consumer” drive and has 1200TBW rating. Since my source is a 40TB array there’s gonna be a lot of TBW going on. I’d like to keep the writing to the RAID array only.

I tried to fix this by moving the duplicati docker volume to the RAID array thinking it was just the docker volume caching but that didn’t fix it. I tried turning off the swap file and that didn’t fix it. I do have 128GB RAM and at any given time I’m only about 2-3gb used (unless running a backup) so I was hoping any caching would be “in memory”. I do see the docker volume will grow to about 5GB memory use which I don’t mind, if there was a way to set caching up in memory I’d be okay with that.

QUESTION: How can I eliminate all of this system-drive writing during backups? I’d like to get the data from the network and write it straight to the RAID array. the RAID array does have a NVMe cache device (read and write) and I do have excess RAM so if there are any settings I can change to keep the writes off my system disk it’d be appreciated. Thanks!

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I believe I found the answer, so instead of deleting my post I’ll go ahead and add here for others:

The fix is to use the tempdir option to change the temp directory from /tmp/ to (in my case) /mnt/volume2/tmp/ to keep all temp writes on the RAID volume.

Apparently there is a lot of writing to the /tmp folder. If anyone knows a way to get it to use the excess RAM I have let me know. I did some monitoring and the duplicati docker container got up to 11GB memory use, which I don’t mind I’m sure if I only had 8GB it wouldn’t get that big. BUT - if there’s a way to get it to use more RAM and avoid any /tmp action I’d be up to learn.

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@JBinFla, assuming you are on linux; read up on tmpfs.
That basically creates a file system in RAM which you can mount and use as scratch space for Duplicati tempdir.

For example you can create this in /etc/fstab:

# <file system>  <mount point>       <type>  <options>           <dump>  <pass>
duplicati_tmp    /mnt/duplicati_tmp  tmpfs   defaults,size=32G   0       0

I have not used duplicati for a while so I do not know if there are any other cache items to take care of. This thread touches on that:

hth.

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