You don't say why you are intending to run data-collect, so I assume that you are intending to run a data collect so that you can submit the data-collect to Veritas Support for either inspection by Veritas Support prior to the upgrade/patch, or simply to act as a "this is the state the appliance was in" before the upgrade. An appliance does not normally need to be completely quiet to run a data-collect.
But if the appliance is a Master Server, or Master/Media Server, then the appliance really does need to be quiesced before being patched or upgraded.
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Some questions:
1) Are you patching or upgrading? I ask because you haven't specified from which version nor to which version. Can you tell us?
2) How many appliances are being upgraded?
3) Is/are the appliance(s) to be upgraded in Media Server only role, or are any in Master Server role, or even Master/Media Server role?
4) Do you have any NetBackup AIR Replication configured?
5) Do you have any separate DR site NetBackup environments?
You've given almost nothing to work with, so, if you'd like some further advice, then please do answer the five questions above and we might be able to help you some more.