I've been fiddling for a bit using the guide on the wiki to get BT5 installed on usb with persistence.

Ran into an issue where I need to copy files from the virtual cdrom (i.e the iso image in vm) to the sdb1 partition I made on the usb key. Seems the 2500M of space allotted isnt enough if I understood the error message correctly.

This is from the wiki tutorial:

The first partition needs to be a primary partition of no more than 2.5 GB and set to type vfat (I have made this partition larger than needed so as it covers all iso's and future versions). Make the partition active to avoid boot problems.
The second Partition which stores the changes should take up the rest of the space on the thumbdrive, or as much as you wish to allocate for saving changes (5GB at an absolute minimum).
is 2.5GB the max for a particular reason?

I'm using an 8gb usb key, would it be worth upgrading and using a 16gb key instead with larger sdb1 partition?

Thanks for the help.