How to use partclone from btrfs to exfat

I have a 4TB SSD to which I’d like to backup my working drive.

Partclone would seem to be the ideal tool to backup a btrfs partition to an exfat drive, but when I run

sudo partclone.btrfs -c -d -s /dev/nvme0n1p3 --overwrite <dirspec>/main_disk.img

I receive the message

Partclone v0.3.27 http://partclone.org
Starting to clone device (/dev/nvme0n1p3) to image (<dirspec>/main_disk.img)
device (/dev/nvme0n1p3) is mounted at /
error exit
Partclone fail, please check /var/log/partclone.log !

The log file contains the same information.

Does anyone have any hints?

Thanks!

Could it be that partclone cannot clone in live? The cloned partition must be umounted.

</dirspec/>

Shouldn’t that be the destination directory?

It is; I edited the string out to keep things shorter.

Huh.

I’ll give that a try.

Thanks!