Hi,
Write failures typically point to some issue with underlying I/O subsystem. I would check the /var/log/messages around the time failure happened. Are these instances running in virtual environment? We have seen cases Vmware marked disks as read-only because I/O controller saturation caused by the backup script.
Also could you confirm if the filesystem where you’re backing up isn’t NFS? sqlite files are known to have issues with NFS implementations - Sqlite NFS FAQ
–
Abhishek