+=item B<Instances> B<integer>
+
+How many read instances you want to use for this plugin. The default is one,
+and the sensible setting is a multiple of the B<ReadThreads> value.
+
+This option is only useful when domains are specially tagged.
+If you are not sure, just use the default setting.
+
+The reader instance will only query the domains with attached matching tag.
+Tags should have the form of 'virt-X' where X is the reader instance number,
+starting from 0.
+
+The special-purpose reader instance #0, guaranteed to be always present,
+will query all the domains with missing or unrecognized tag, so no domain will
+ever be left out.
+
+Domain tagging is done with a custom attribute in the libvirt domain metadata
+section. Value is selected by an XPath I</domain/metadata/ovirtmap/tag/text()>
+expression in the I<http://ovirt.org/ovirtmap/tag/1.0> namespace.
+(XPath and namespace values are not configurable yet).
+
+Tagging could be used by management applications to evenly spread the
+load among the reader threads, or to pin on the same threads all
+the libvirt domains which use the same shared storage, to minimize
+the disruption in presence of storage outages.
+