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Subject: Re: zfs, iSCSI and volmode=dev
To: freebsd-stable@freebsd.org
References: <ece540ba-8039-424f-8bad-c4266d70d84b@norma.perm.ru>
From: Pete French <petefrench@ingresso.co.uk>
Message-ID: <203bd4d2-8c12-620a-8d0c-5c76d279174c@ingresso.co.uk>
Date: Mon, 4 Sep 2017 15:25:18 +0100
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> 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.