Author: Rich Language: text
Description: ZFS - Copy on Write and Virtual Machines. Timestamp: 2014-07-03 19:30:56 +0000
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  1. I've moved my VirtualBox VM images to my FreeNAS 9.2.x which is SuperMicro based Core i3 with 32GB DDR3 ECC RAM using 4 drive ZFS Raid Z2 based on WD Red 4TB NAS drives. I understand that ZFS will make a copy of a file and write changes to the copy.
  3. How does this work with large files such as virtual machine images? Does it just make one copy on write? Is it constantly making copy on write images? If my VM images are 100GB is FreeNAS constantly making 100GB file copies?
  5. I have a Core i7 based desktop with Samsung SSD drive running Antergos with Virtual Box. The VM images are accessed via NFS to the FreeNAS. I observe significantly more FreeNAS disk activity than the VirtualBox disk activity icon shows. For example a couple of small blimps on VirtualBox disk icon results in the FreeNAS disk indicator light pegged solid for a while.
  7. Overall performance is very acceptable unless I leave the VM idle for a bit. Then when I try to use it the VM it appears to hang for a few seconds (under 10) and the FreeNAS light is pegged again until the VM comes back to life. I'm guessing the pause is FreeNAS making another 100GB copy on write.
  9. I assume this is normal behavior, just looking to understand what is going on in the background. It may impact how many VMs I fire up concurrently from the FreeNAS.
  11. While this configuration is currently for my own private use, I do plan on offering this to my clients in the future.
  13. Thanks in advance. Long time listener who has enjoyed the entire back catalog of LAS, Unplugged, TechSnap, SciByte, Unfiltered and working my way through BSD Now.
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