Zvol Question

[sidisalim]

I am a newbie to FN. I just setup FN v11. I setup a Zvol and Configured iSCSI for my ESXI host. I was able to add a datastore and connect successfully. I also successfully migrated a couple of VMs. I am just curious about where the VM files are store on the Zvol I created. How is the data stored? Any details you can provide are appreciated.

Thanks,

 

[Stux]

I am a newbie to FN. I just setup FN v11. I setup a Zvol and Configured iSCSI for my ESXI host. I was able to add a datastore and connect successfully. I also successfully migrated a couple of VMs. I am just curious about where the VM files are store on the Zvol I created. How is the data stored? Any details you can provide are appreciated.

Thanks,

The VM files are stored *in* the zvol. The zvol is a virtual block device, ie like a harddrive, and ESXi treats it as a harddrive. Theoretically you could mount the zvol in a different OS which understands VMFS, and see the files. If you actually want to see the files, then you will need to use NFS instead of iSCSI, or use the ESXi databrowser.

So, in that virtual block device, ESXi formats it as VMFS, then creates VMDKs, which it then passes to your VMs...

 

[sidisalim]

Thanks for the Clarification Stux!

I setup the Volume as a Zvol vs. NFS based on some comments I saw on a FN forum talking about poor performance with NFS. Can you confirm as well?

Also. What would be a good use case for me to setup datasets based on my Zvol config? Are there any benefits with Datasets?

- I have 2 (3 TB) Drives / Mirrored
- I am only using 1 TB for the first Zvol (The one that ESXI is connected to via iSCSI)

Any thoughts on that would be great.

Thanks in advance!

 

[IceBoosteR]

Hi,
NFS is way more "safer" as iSCSI. This is because NFS writes synchonously to your FreeNAS Server, and to confirm that the data is transmitted, this needs a lot of time. You can tune this behaviour in using a dedicated SSD for SLOG. You can find some information here:
https://forums.freenas.org/index.ph...-from-esxi-5-1-everything-else-is-fast.10448/
https://www.reddit.com/r/homelab/comments/47jvli/slow_freenas_performance/
On the other hand, iSCSI writes asynchronous, so does not wait for FreeNAS to confirm if the data is transmitted. In case of a power loss, you can loose data or corrupt a VM. But for me I also use iSCSI because rebuilding the VMs is easy, and I do not need to see the data on the FN Server itself.
Yes you can put a ZVOL under a dataset - you can better organize your data if you whish. You can enable dedup by default on the ZVOL, but if you want to use an other compression algorythm, as the pool default is, you might wanna use a dedicated dataset to activate GZIP for example for the underlaying zvol. * BUT I AM NOT 100% sure if this works *

Please keep in mind that expanding the ZVOL does not increase the datastore on ESXi. I did this and it was a hell to increase this on ESXi side. ESXi see another partition, and is not able to rezize the datastore (VMWare- why??? )
So I ended up creating a new ZVOL and transfering all the data from the smaller one to the bigger one. Maybe someone out there is smart enough to rezize it - so plan for the future, or use different ZVOLs if you want to keep things easy.

Rgs,
Ice

 

[sidisalim]

Ice,

Thanks for your feedback. Very helpful

Cheers!

 

[IceBoosteR]

Ice,

Thanks for your feedback. Very helpful

Cheers!

Hi,
you're welcome ;)