How to transfer a large amount of files from one disk to another?

Question

linux

In general, there is a server on which the site. It stores user data. There are already over 3 million files. ~2TB volume. The data is of course updated and replaced.
The disk is almost full.
The task is to add a hard drive to a server and transfer this data to it without stopping the site.
Google and a search on the toaster made it clear that I need to install synchronization applications, but again there are so many of them and it’s not entirely clear whether I need it.
Please help me choose the right path. and choose an application that will solve my problem and cope with such volumes.

Answer 1

rsync. Old proven admin hammer.
0) Mount both disks
1) do rsync
2) repeat the command above until the operating time reaches some acceptable interval
3) close the work with files, it is better to remount the old disk in ro
4) another rsync
5) unmount old disk, remount the new disk in place of the old one
6) open the work with files back
In case of further expansion of the disks, put LVM on top of the new disk. If the old disk already has LVM, then regular pvinit, vgextend, pvmove, lvresize, vgreduce, pvremove, resizefs
If you still have a server, then find out what the raid costs. For software linux raid , disks can be deliveredlarger capacity without downtime.

Answer 2

rsync