zfs, iSCSI and volmode=dev

[Pete French]

> I have an iSCSI production system that exports a large number of zvols 
> as the iSCSI targets. System is running FreeBSD 11.0-RELEASE-p7 and 
> initially all of the zvols were confugured with default volmode. I've 
> read that it's recommended to use them in dev mode, so the system isn't 
> bothered with all of these geom structures, so I've switched all of the 
> zvols to dev mode, then I exported/imported the pools back. 
> Surprisingly, the performance has fallen down like 10 times (200-300 
> Mbits/sec against 3-4 Gbits/sec previously). After observing for 5 
> minutes the ESXes trying to boot up, and doing this extremely slowly, I 
> switched the volmode back to default, then again exported/imported the 
> pools. The performance went back to normal.

I too ghave a number of zvols exportes as iscsi, and I was using dev 
mode util I read this. AM going to experiment with switching back to 
default mode to see what happens. I also use dev mode for my virtualbox 
drives. Am going to try and test that too and see what I get.

Interesting result though...

-pete.