iSCSI/ZFS strangeness

[Steven Hartland]

On 29/10/2015 06:42, Ben RUBSON wrote:
>> Le 29 oct. 2015 à 03:26, Philip Murray <pmurray at nevada.net.nz> a écrit :
>>
>>
>>> On 29/10/2015, at 2:57 PM, Michael W. Lucas <mwlucas at michaelwlucas.com> wrote:
>>>
>>> Hi,
>>>
>>> I'm experimenting with iSCSI HA with FreeBSD 10.2 amd64. I know people
>>> do this sort of thing, but I can't figure out what I'm missing. (Most
>>> of the tutorials cover HAST instead). I suspect the real problem is
>>> "Lucas doesn't know the right search terms."
>>>
>>> The goal is to make an iSCSI-based ZFS pool that's available to two
>>> separate hosts, and remains available even if one of the iSCSI servers
>>> fails. Instead, the pool hangs when either of the iSCSI servers goes
>>> down.
>> I’m no expert and have never used iSCSI and FreeBSD before, but I think you might
>> want to look at the kern.iscsi.fail_on_disconnection sysctl.
>>
>> man 4 iscsi
>>
>> That means the devices will fail instead of hang, and ZFS might decide to mark those
>> devices as faulted instead of waiting for them to respond.
> Hi,
>
> Yes, kern.iscsi.fail_on_disconnection=1 in sysctl.conf will do the trick.
> In addition, you can tune the following to minimize the impact / freeze when iSCSI fails :
> kern.iscsi.ping_timeout=10
> kern.iscsi.iscsid_timeout=10
> kern.iscsi.login_timeout=10
>
> In addition, in ctl.conf, perhaps you should use one target instruction per disk.
> I began with all my disks/luns into a unique target configuration, but when a disk fails and you replace it, you need to refresh the iSCSI configuration using iscsictl -M. At this moment you will loose the connection to all disks, leading into many ZFS devices failed...
> So I think a target per disks is better, then you only refresh the dead target : iscsictl -M -i <the_target_session>
>
> And last thing, thank you very much for your quality books, a must-have :)
>
While not strictly a pure ZFS solution, if your initiators can't both be 
active at the same time a better solution might be to use geom multipath 
with ZFS on top of that?

     Regards
     Steve