thanks for your help. To eliminate as much garbage as possible form the log files (as I may have appended some incorrect information), I cleared all logs and then rebooted - it took around 6 minutes on the nested esxi box... the bulk of the time was spend during the iscsi phase after vmw_satp_alua loaded successfully message on the console. On a UCS blade, this process takes aorund 15 minutes, on a DL360G7 the process takes around 30 minutes - see
http://communities.vmware.com/thread/326077?tstart=0
I've summarised the logs as a single small attachment.
When I look closely at the vmkernel.log file I see the bulk of the time is spent in this section;
<pre>
...
...
2011-09-14T04:50:40.503Z cpu0:2604)ScsiDevice: 3121: Successfully registered device "naa.600144f02aa50c0000004e640a430001" from plugin "NMP" of type 0
2011-09-14T04:50:40.524Z cpu0:2604)FSS: 4333: No FS driver claimed device 'mpx.vmhba32:C0:T0:L0': Not supported
2011-09-14T04:50:40.555Z cpu0:2604)VC: 1449: Device rescan time 20 msec (total number of devices 5)
2011-09-14T04:50:40.555Z cpu0:2604)VC: 1452: Filesystem probe time 29 msec (devices probed 5 of 5)
2011-09-14T04:50:43.471Z cpu0:2050)LVM: 13188: One or more LVM devices have been discovered.
2011-09-14T04:51:06.754Z cpu1:2604)FSS: 4333: No FS driver claimed device 'mpx.vmhba32:C0:T0:L0': Not supported
2011-09-14T04:51:06.775Z cpu1:2604)VC: 1449: Device rescan time 22 msec (total number of devices 5)
2011-09-14T04:51:06.775Z cpu1:2604)VC: 1452: Filesystem probe time 19 msec (devices probed 5 of 5)
2011-09-14T04:51:32.987Z cpu0:2604)FSS: 4333: No FS driver claimed device 'mpx.vmhba32:C0:T0:L0': Not supported
...
</pre>
For some reason, it looks like it is repeatedly trying to access vmhba32 which appears to be the controller the CDrom device is hanging off. sigh,..
I guess this is a bug in vsphere5? Please advise.