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In some cases an in-place upgrade can be applied with the advantage to require less time and to keep all (or most) of the settings and configurations. For example, a vCenter Server 4.1 can be directly updated to the 5.1 version (the requirements of the two versions are quite the same) or an old ESXi can be updated to ESXi 5.
But in most cases, also when the in-place upgrade is possible, could be interesting considering a full reinstallation, that give the advantage of the new clean situation. Also it can require more time (and more effort), but can give less downtime, because for example you can build a new vCenter Server, configure it and then simple re-connect the hosts to this new one.
Anyway, some points are quite common for each major vSphere upgrade:
- HCL: the Hardware Compatibility List must be checked before each upgrade (each vSphere major release as a specific HCL that could be different). Also the software part must be checked (on the VMware Product Interoperability Matrix) to verify the compatibility of some specific part (like for example the DBMS).
- Firmware: this aspect is related to the previous point… each major release can require a minimum firmware level (especially for servers and storage)… usually a good approach could be update to latest stable firmware (but check with vendor recommendation).
- ESX: in can be upgrade (with an in-line process) to ESXi 5… but only in some cases (for example not when ESX was upgraded from version 3.x)… and is not possible change the destination of the installation (that goes in the boot partition). Usually a rebuild could be a better option.
- Drivers and modules: some 3rd part modules or drivers can prevent an upgrade of ESXi /ESX. Check their compatibility with ESXi 5 and, if needed, remove them before the upgrade.
- Plugin: the vCenter plugins must be verified before the upgrade of vCenter Server… both on the server-side and the client-side. In most cases, could be better remove them before the upgrade.
- Converter Enterprise e Guided Consolidation: those plugin does no more exist in vSphere 5. Remove them before upgrade the vCenter Server (otherwise follow this guide).
- VDR: has been replaced with VDP.
- View: you need to upgrade it to View 5.1 (as described in this post).
- SRM: same as View. You need to upgrade it to SRM 5.1 (as written in this post).
For more information see also:
Issues with vSphere 5.1?
Actually vSphere 5.1 is more than a minor release (see also: VMware version numbering: is .1 a minor release?) and there are some issues, most corrected with the 5.1a and 5.1b version, but other still present:
- during the upgrade from 5.0 a warning of a non valid vCenter license is prompted, but the license is keeped correctly
- DVS and beaconing togheter have a big issue (see this post)
- dropped packets counter is wrong (at vNIC level)
- some issues with graphs (see the note in the download page)
- snapshot alarms are triggered, but they does disappear, also when status goes back to green; see also KB 2037464
See also: VMware vSphere 5.1 Known Issues.