Differential D19357 Diff 46307 src/docs/user/cluster/cluster_repositories.diviner

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src/docs/user/cluster/cluster_repositories.diviner

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	this process. For example, loading the most recent backup snapshot onto the new			this process. For example, loading the most recent backup snapshot onto the new
	device will substantially reduce the amount of data that needs to be			device will substantially reduce the amount of data that needs to be
	synchronized.			synchronized.


	Contracting a Cluster			Contracting a Cluster
	=====================			=====================

	To reduce the size of an existing cluster, follow these general steps:			If you want to remove working devices from a cluster (for example, to take
				hosts down for maintenance), first do this for each device:

	- Disable the bindings from the service to the dead device in Almanac.			- Change the `writable` property on the bindings to "Prevent Writes".
				- Wait a few moments until the cluster synchronizes (see
				"Monitoring Services" below).

				This will ensure that the device you're about to remove is not the only cluster
				leader, even if the cluster is receiving a high write volume. You can skip this
				step if the device isn't working property to start with.

				Once you've stopped writes and waited for synchronization (or if the hosts are
				not working in the first place) do this for each device:

				- Disable the bindings from the service to the device in Almanac.

	If you are removing a device because it failed abruptly (or removing several			If you are removing a device because it failed abruptly (or removing several
	devices at once) it is possible that some repositories will have lost all their			devices at once; or you skip the "Prevent Writes" step), it is possible that
	leaders. See "Loss of Leaders" below to understand and resolve this.			some repositories will have lost all their leaders. See "Loss of Leaders" below
				to understand and resolve this.

				If you want to put the hosts back in service later:

				- Enable the bindings again.
				- Change `writable` back to "Allow Writes".

				This will restore the cluster to the original state.


	Monitoring Services			Monitoring Services
	===================			===================

	You can get an overview of repository cluster status from the			You can get an overview of repository cluster status from the
	{nav Config > Repository Servers} screen. This table shows a high-level			{nav Config > Repository Servers} screen. This table shows a high-level
	overview of all active repository services.			overview of all active repository services.
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