Commit 0102e732 authored by Klaus Aehlig's avatar Klaus Aehlig
Browse files

Update design document for hroller



The requirement to be able to plan full node evacuation came up after
the initial design. So add a section describing the algorithm, if
full evacuation is requested.
Signed-off-by: default avatarKlaus Aehlig <aehlig@google.com>
Reviewed-by: default avatarMichele Tartara <mtartara@google.com>
parent 9353adde
......@@ -123,6 +123,17 @@ algorithm might be safe. This perhaps would be a good reason to consider
managing better RBD pools, if those are implemented on top of nodes
storage, rather than on dedicated storage machines.
Full-Evacuation
+++++++++++++++
If full evacuation of the nodes to be rebooted is desired, a simple
migration is not enough for the DRBD instances. To keep the number of
disk operations small, we restrict moves to ``migrate, replace-secondary``.
That is, after migrating instances out of the nodes to be rebooted,
replacement secondaries are searched for, for all instances that have
their then secondary on one of the rebooted nodes. This is done by a
greedy algorithm, refining the initial reboot partition, if necessary.
Future work
===========
......
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