I use Open-E in production on standard Intel (Supermicro) hardware. It
can work in A/A (only in respect of ovirt, ie one LUN normally active on
one server, the other LUN normally stays on the the other node) or A/P
mode with multipath. Even in A/P mode it fails over quick enough to
avoid VM pauses, using virtual IPs that float between the nodes. These
modes are supported for both iSCSI or NFS.
I've also successfully implemented the same kind of rapid failover using
standard linux HA tools (pacemaker and corosync). I've had migration
times under 2s.
NFS has the added complications of filesystem locking. Maybe some of the
docs on the CTDB site will help, as they ensure that NFS will be running
on the same ports on each host and locking DBs will be shared between
the two hosts. I have no idea if TrueNAS supports CTDB or similar
distributed locking mechanisms.
Caveat: this is with iSCSI resources. I've not really run VMs in oVirt
in anger against any kind of NFS storage yet. My boss wants to try
Tintri, so I'll see how that works.
Cheers
Alex
On 06/06/17 18:45, Matthew Trent wrote:
Thanks for the replies, all!
Yep, Chris is right. TrueNAS HA is active/passive and there isn't a way around
that when failing between heads.
Sven: In my experience with iX support, they have directed me to reboot the active node to initiate
failover. There's "hactl takeover" and "hactl giveback" commends, but reboot
seems to be their preferred method.
VMs going into a paused state and resuming when storage is back online sounds
great. As long as oVirt's pause/resume isn't significantly slower than the
30-or-so seconds the TrueNAS takes to complete its failover, that's a pretty
tolerable interruption for my needs. So my next questions are:
1) Assuming the SAN failover DOES work correctly, can anyone comment on their
experience with oVirt pausing/thawing VMs in an NFS-based active/passive SAN
failover scenario? Does it work reliably without intervention? Is it reasonably
fast?
2) Is there anything else in the oVirt stack that might cause it to "freak out"
rather than gracefully pause/unpause VMs?
2a) Particularly: I'm running hosted engine on the same TrueNAS storage. Does
that change anything WRT to timeouts and oVirt's HA and fencing and sanlock and
such?
2b) Is there a limit to how long oVirt will wait for storage before doing
something more drastic than just pausing VMs?
--
Matthew Trent
Network Engineer
Lewis County IT Services
360.740.1247 - Helpdesk
360.740.3343 - Direct line
________________________________________
From: users-boun...@ovirt.org <users-boun...@ovirt.org> on behalf of Chris Adams
<c...@cmadams.net>
Sent: Tuesday, June 6, 2017 7:21 AM
To: users@ovirt.org
Subject: Re: [ovirt-users] Seamless SAN HA failovers with oVirt?
Once upon a time, Juan Pablo <pablo.localh...@gmail.com> said:
Chris, if you have active-active with multipath: you upgrade one system,
reboot it, check it came active again, then upgrade the other.
Yes, but that's still not how a TrueNAS (and most other low- to
mid-range SANs) works, so is not relevant. The TrueNAS only has a
single active node talking to the hard drives at a time, because having
two nodes talking to the same storage at the same time is a hard problem
to solve (typically requires custom hardware with active cache coherency
and such).
You can (and should) use multipath between servers and a TrueNAS, and
that protects against NIC, cable, and switch failures, but does not help
with a controller failure/reboot/upgrade. Multipath is also used to
provide better bandwidth sharing between links than ethernet LAGs.
--
Chris Adams <c...@cmadams.net>
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