We have found that certain 4kn drives from Seagate and WesternDigital have issues with some Synology DS/RS units that cause intermittent reboots and volume corruption.
A typical example of this is the Western Digital WD100EFAX or Seagate ST10000VN0004 10TB drives, both of which will only work reliably in some units with Write Cache Disabled. Unfortunately disabling the write cache has a negative impact on performance so this is not a recommended outcome. We have raised this issue with Synology who are looking into it.
When in operation the synology unit will loose the ability to write to the drives causing a kernel panic and a reboot. By directing the logging output (both kern, messages and syslog) to a mounted USB drive we can capture the actual event that is otherwise lost.
Write cache is handled by the drives so this may be an interface ↔ drive controller issue probably timing related but without tearing down the hardware there's no easy way to know.