Revisit of iSCSI Extent vs File for ESXi for Truenas 12 U8

[Zubin Singh Parihar]

Hey Folks,

I wanted to revisit this because all the posts I read about this topic is very old.

I'm running Truenas 12 U8

I'm building an iSCSI datastore for my ESXi lab.
Should I build iSCSI as a ZVOL Device Extent of File Extent?

Please advise and why? (Performance, speed, flexibility, features, etc).

Cheers!

 

[HoneyBadger]

ZVOL, my understanding is that not only are they more performant but file extents do not get full VAAI support.

Please note that in either case, you will have "default unsafe writes" with sync=standard. I know it's a lab but just take that into consideration for your lab backup strategy.

 

[Zubin Singh Parihar]

ZVOL, my understanding is that not only are they more performant but file extents do not get full VAAI support.

Please note that in either case, you will have "default unsafe writes" with sync=standard. I know it's a lab but just take that into consideration for your lab backup strategy.

What should "sync" be set to??

 

[HoneyBadger]

What should "sync" be set to??

For safety, iSCSI ZVOLs and datasets backing file-based extents need to be set as sync=always - this will negatively impact performance unless your pool devices are capable of handling O_SYNC writes at high speed/low latency, and/or you have an SLOG device capable of that.

Leaving it set as sync=standard causes your writes to be staged in RAM only on ZFS, which could cause data loss in a power outage or unexpected shutdown.

 

[Zubin Singh Parihar]

Thank, I appreciate this recommenation!
I'm really happy that it was very easy to make this change by editing the ZVOL (instead of having to recreate it)