VM restore options - /var/tmp


New Member
Jul 10, 2023
Today I was moving some VM's manually between servers via backup&restore, and I noticed that my system copies the dump file all okay between servers, but when I start the restore process, it is really sluggish and my I/O wait time increases.

This is more of an intro to my actual question, but still I think it's worth to know:
  • I have one storage group, with two 2TB Exo HDD's configured under Software RAID1 and LVM on top of that <- this is where my OS and backups reside
  • Copying backups to the above storage occurs at full gigabit speed (~100MiB/s)
  • I have SSD disk configured for my VM storage <- this is where I'm restoring my backups
  • Proxmox 8
The very slow restore actually gave me a lot of headache not only today but on some other servers i've configured but i never paid much attention to it until today, since the server is brand new with 256Gigs of RAM and single socket AMD EPYC 7543P 32-Core Processor.

My investigation lead me to this process:

/bin/bash -c set -o pipefail && cstream -t 83886080 -- /mnt/dumpy/dump/vzdump-qemu-124-2023_07_10-20_09_57.vma | vma extract -v -r /var/tmp/vzdumptmp32211.fifo - /var/tmp/vzdumptmp32211

As you can notice, vma extract uses /var/tmp which is NOT tmpfs and uses persistent storage, in this case, my spinning plate HDD's. It'd introduce mix of Read/Write operations that would explain the slowliness of the whole proccess.

Could this be switched to just /tmp ?


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