Hi Alexander,
Do you think this is a reliable perfomant solution to copy big files (can not specifiy how big am, but could be estimated more than 500MB ) - possible limitations in xquery ?
I would say so. Some bulk operations are only available via commands, but a lot of functionality for commands and XQuery is based on the same code. To reduce memory consumption, you can enable the ADDCACHE option [1], but it will slow down the execution a bit.
As databases are lightweight objects in BaseX, you can also write all your files to a dedicated backup database.
Best, Christian