I have a freenas box that I use to back ESX VMs to but don't have a SLOG yet and thus speed is poor due to ESX pushing sync writes to the NFS store on my freenas box.

If I created a separate dataset for the share and set sync=disabled for just that dataset will I be able to contain corruption to just that dataset if I loose power mid-write or will the entire ZFS pool still be at risk to corruption?

  • Surprised you'd ask here and not ServerFault.com – ewwhite Dec 3 '15 at 16:42
  • I completely agree. My bad. Not sure of the way to get it moved over to ServerFault but I think this is a pretty important question about a common ZFS use case. I have found quite a lot of posts stating that it is very dangerous to enforce sync. Most posts do not appropriately qualify the actual risks or outline ways to reduce them. – Timothy C. Quinn Dec 15 '15 at 3:20
  • I'd recommend you read this article on the ZIL and what it really means. See here. – ewwhite Dec 15 '15 at 3:21
  • Wow. What a read! Andrew is a very clear writer and definitely one I will follow. Sure am glad I'm just using FreeNas for read centric or write centric data. I was worried about running VMs and Andrews information confirmed this. Thanks! – Timothy C. Quinn Dec 15 '15 at 3:51

Due to a delay in getting a response from this forum, I decided to post the question to the FreeNAS forums. Dru Lavignue from iXSystems reponded with the following answer:

If you set a property on a dataset, only that dataset (and its child datasets that aren't explicitly set differently) is affected by the ramifications of that property.

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