[lustre-discuss] MGS IP in a HA cluster

Ms. Megan Larko dobsonunit at gmail.com
Mon Feb 22 13:31:00 PST 2021

Hello Community!

WRT Mr. Sid Young's question on volumes visible to HA partner for failover,
I have experience with lustre-2.12.6 that is ZFS-backed.  We have the
MGS/MDS and then the OSS boxes in pairs using a heartbeat IP
crossover-cabled between the two members in the pair; there is a unique
non-routeable IP assigned to each member of the HA pair.  The PCS set-up
defines a preferred node for a Lustre target (MDT/OST).  If the preferred
node of the pair is unavailable on the primary then the zpool is acquired
via pacemaker on the secondary which is capable of hosting its own OSTs and
those of its HA partner if necessary.

Our MDS HA is different.  We have only one MDT which is mounted on one and
only one member of the MGS/MDS HA pair.

Generally-speaking, one does not want a multi-mount situation.   A target
should only be on one member of the pair.   For our HA pairs, the "zpool
list" or "zpool status" does not even display a zpool which is not active
(already imported) on that particular box.   Yes, the pairs may have access
to the resources of the partner, but that does not mean that those
resources are active/seen/visible on the secondary if they are active on
the primary.   If the primary is inactive then yes all target resources
should be visible and active on the secondary member of the HA pair.

Just sharing our viewpoint/use case.
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