On the impact of two-level directory structure for storing blobs

[Alexey]

I would suggest to use LVM before ext4, it would allow to move data much more faster between disks.
See

Best Practice for Transferring Data To New Drive

It’s not difficult, but requires to read a documentation. I would emulate this on loop devices Create images for the disks $ truncate -s 1G disk1.raw $ truncate -s 1G disk2.raw Create loop devices to emulate disks $ sudo losetup -f disk1.raw $ sudo losetup -f disk2.raw find which one loop devices has been created $ losetup | grep disk /dev/loop6 0 0 0 0 /home/ubuntu/disk1.raw 0 512 /dev/loop7 0 0 0 0 /home/ubuntu/disk2.ra…

However, you likely use ZFS, so for you it should be simple too, just send and receive a snapshot, then stop the node and send another one to finish a migration, then start the node on a new dataset.