I have two FAS2554 systems (each with 2 controllers) in two different racks (racks are next to each other). I want to set them up so if one system fails it automatically failsover to the other one. What would be the recommended way of doing this? Do I need MetroCluster or is clustered data ONTAP enough? I want one whole NetApp to be a mirror of the other.
Automatic switchover with storage system available only with MetroCluster (HA technology).
Metro cluster available with both 7-mode and Cluster-Mode.
MetroCluster available to all AFF & FAS systems except low-end systems like FAS 2XXX or AXX.
Why is it not available to low-end systems? Because of MC require at least an additional special PCIe card to be installed in controllers.
In your case, you can configure and use storage manual or semi-manual (Depending on your environment) switchover with a DR technology called SnapMirror.
Why you can't have automatic storage switchover with SnapMirror out of the box like with MC? Because of SnapMirrot designed and build for different purposes and requirements that MCC, though both are data protection technologies. SnapMirror can be used with MC to add an additional layer of data protection and cannot replace MC, in short, because of DR architecturally different that HA.
You can indeed upgrade your FAS2000 systems with latest ONTAP Cluster-Mode software and then join them in a Cluster (you will need two 10GB cluster switches).
But you should not mix up that kind of Clusterization with MetroCluster.
MetroCluster is a Data Protection technology (it automatically switch between sites in case of disaster)
While Cluster-Mode Clusterization is single namespace technology which allows you to migrate data across nodes in your cluster nondisruptively, it does not provide automatic or any kind of data protection functionality like MC for example.