DMA errors
A big performance increase for RAID5 systems: use 'noatime' in fstab. or: mount / -o remount,noatime This way every read does not result in an update of the 'access-time' which is a write as well.
Wear out after 1,000 to 10,000 write cycles for MLC, up to 100,000 write cycles for SLC.
run unison in batch-mode (pref-file: batch = true) and there will be no questions and auto-sync all updates and skip all conflicts. When minimum one conflict is seen, exit code is non-zero and messages are sent to stderr (crontab would pick that up and sent email)