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Date: Thu, 2 Jun 2016 17:50:28 +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 Thu, Jun 02, 2016 at 12:12:35PM +0500, Eugene M. Zheganin wrote:

> Hi.
> 
> On 01.06.16 18:23, Slawa Olhovchenkov wrote:
> >
> > 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.
> If you mean that I should distribute the HAST one-disk device via iSCSI
> and then use it as a half of zfs mirrored pool on each node, then I
> should ask how the pool will decide which half is more recent - local or
> iSCSI, after I will import it and the kernel will found that it's vdevs
> differs a lot ? And why should I prefere this overcomplicated scheme
> over the geom_mirror, which seems rather simple when comparing. Seems
> like I can point HAST to /dev/mirror/whatever device, right ?

I am suggesting next setup:

node0:
  own pool zroot0: mirror-0: local_disk0
      	   	   	     remote-iscsi_disk1/1
  local_disk1: exported by iscsi as remote-iscsi_disk0/1 to node1

node1:
  own pool zroot1: mirror-0: local_disk0
      	   	   	     remote-iscsi_disk0/1
  local_disk1: exported by iscsi as remote-iscsi_disk1/1 to node0


No HAST.
Disks synced by ZFS over iSCSI.