Esxi 6.7 + iSCSI zvol share - Immediately shows "Normal, Degraded" in Vsphere

[kdragon75]

I have a similar setup but Im using 8gb fibre channel. I can easily saturate each port when running high queue depth sequential IO benchmarks in VMs at least for reads. With my SLOG i get about 500MB/s writes under the same IO profile.

 

[SmoothRunnings]

You beat me to my edit. What can you tell me about your testing methods? Also is your iSCSI vdev set to sync always? Because it should be. It will also kill write performance.

I am still very new to this. So all I have don't is watch the graphs under reports. Another person suggested I try the AutoTune option under System -> Advanced which has seem to help a bit. Not sure what the iSCSI vdev part, maybe you can direct me were I can see it so I can better tell you?

Thanks

 

[kdragon75]

If you look understarage and see all of your datasets, if you select the vdev you used (iscsivol in your case) and select the wrench icon (edit) its in there. FreeNAS Docs - zvol
If your just booting VMs and watching the graph, it will only show what the host needs to boot the VMs. If you have a windows VM download CrystalDiskMark and run a test at least 4GB. post teh screenshot.

 

[SmoothRunnings]

If you look understarage and see all of your datasets, if you select the vdev you used (iscsivol in your case) and select the wrench icon (edit) its in there. FreeNAS Docs - zvol
If your just booting VMs and watching the graph, it will only show what the host needs to boot the VMs. If you have a windows VM download CrystalDiskMark and run a test at least 4GB. post teh screenshot.

Ok, so you said look under storage(?) ... If I select vdev? I dont see any vdev

 

[kdragon75]

I'm sorry. I meant to say zvol. iscsivol is a zvol.

 

[SmoothRunnings]

I'm sorry. I meant to say zvol. iscsivol is a zvol.

I see what you mean now. My sync is set to Inherit (Standard), should I be setting it Always?
Oh and it looks like compression is turned on it.. it shows lz4 under compression for my zvol

Thanks,

 

[kdragon75]

Generally lz4 is prefered for almost every case. I turn it off for my backup data sets as the data is already heavily compressed and lz4 save no space and wastes CPU. On my zvol for vmware, I have some nice savings. Its somewhere around 1.5x compression with about 15 windows VMs.

As for the sync setting, you need to do some reading on what sync vs async writes are and how this can impact ZFS.
http://doc.freenas.org/11/zfsprimer.html
https://docs.oracle.com/cd/E19253-01/816-4854/character-11/index.html
https://pthree.org/2013/04/19/zfs-administration-appendix-a-visualizing-the-zfs-intent-log/
In short, async writes lie. It says the data is safe on disk before it is. Sync writes do not, they wait until the data is safe on disk wether on a SLOG or the pool. If you have any issues with the connection to your storage and defiantly if you lose power, you WILL have some file system corruption on your VMs