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Date: Wed, 1 Jun 2016 16:23:00 +0300
From: Slawa Olhovchenkov <slw@zxy.spb.ru>
To: "Eugene M. Zheganin" <emz@norma.perm.ru>
Cc: stable@freebsd.org
Subject: Re: HAST, zfs and local mirroring
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On Tue, May 31, 2016 at 11:18:32PM +0500, Eugene M. Zheganin wrote:

> Hi.
> 
> I wat to start using HAST, I have two nodes and a pair of disk on each 
> node. So I want to use HASt in an environment where each HAST resource 
> would be mirrored. What is the preferred approach if I want to use ZFS 
> on an end-device to avoid exsessive fscking, and, in the same time, I 
> want to have some redundancy on a block level ? I see two possibility: 
> HAST on a zvol of a mirrored pool, and a ZFS on a hast. But recently I 
> heard that nested zfs (like zfs on zvol) is clamed unsupported. 
> Futhermore, I have zfs on a geli on a zvol, and this solution proved 
> itself to be very affected to livelocking - when disk i/o on a such fs 
> is above some treshold, system is locking, and the only way out is to 
> reset it. Should I chose geom_mirror to provide a device for HAST and 
> the build ZFS on it ?

Only FS support changed data bypass FS layer is Files-11 ODS-2 level,
may be hardware support required.

Can you use ZFS mirror with one vdev local and other vdev by iSCSI?
Every node using separate ZFS pool in this case.