Looking forward to SharePoint 2010? Wondering how long it will take to upgrade your 600 GB-worth MOSS farm? How about 50'000 site collections? Well, the truth is no one can predict it for you. Even if you ask Sean Livingston, the Program Manager for SharePoint upgrade at Microsoft, his response will most likely vary between "I don't know" to "it depends". The upgrade performance depends on the structure of your SharePoint databases and the hardware that powers your farm. You cannot really derive your upgrade time based on someone else's experience. Doing a test upgrade on a copy of your own database is the only way to get accurate numbers.
However, Sean's SPC09 Advanced Upgrade session provides an interesting insight into what factors impact upgrade performance most both on the database and hardware sides. These findings are based on Microsoft's own tests and order the factors by their impact (most to least) on the upgrade time:
So the database size doesn't matter all that much! Sounds counterintuitive, right? But if you think about it, the upgrade process upgrades objects, not BLOBs. So it doesn't care how big the database is but how many content items it holds.
Another good point is that on the hardware side, SQL is the king. Well, that shouldn't come as a surprise to SharePointers at all. Fast disk I/O ensures great upgrade speed for your databases.