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Subject: Re: Storage 'failover' largely kills FreeBSD 10.x under XenServer?
To: Karl Pielorz <kpielorz_lst@tdx.co.uk>,
 =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>
Cc: freebsd-xen@freebsd.org
References: <62BC29D8E1F6EA5C09759861@[10.12.30.106]>
 <20170920114418.pq6fhnexol2mvkxv@dhcp-3-128.uk.xensource.com>
 <E20E34C4D5A766D4854317A5@Mac-mini.local>
From: Miroslav Lachman <000.fbsd@quip.cz>
Message-ID: <59C287E2.1030500@quip.cz>
Date: Wed, 20 Sep 2017 17:23:14 +0200
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Karl Pielorz wrote on 2017/09/20 16:54:
>
>
> --On 20 September 2017 at 12:44:18 +0100 Roger Pau Monné
> <roger.pau@citrix.com> wrote:
>
>>> Is there some 'tuneable' we can set to make the 10.3 boxes more tolerant
>>> of the I/O delays that occur during a storage fail over?
>>
>> Do you know whether the VMs saw the disks disconnecting and then
>> connecting again?
>
> I can't see any evidence the drives actually get 'disconnected' from the
> VM's point of view. Plenty of I/O errors - but no "device destroyed"
> type stuff.
>
> I have seen that kind of error logged on our test kit - when
> deliberately failed non-HA storage, but I don't see it this time.
>
>> Hm, I have the feeling that part of the problem is that in-flight
>> requests are basically lost when a disconnect/reconnect happens.
>
> So if a disconnect doesn't happen (as it appears it isn't) - is there
> any tunable to set the I/O timeout?
>
> 'sysctl -a | grep timeout' finds things like:
>
>   kern.cam.ada.default_timeout=30


Yes, you can try to set kern.cam.ada.default_timeout to 60 or more, but 
it can has downside too.

Miroslav Lachman