Regarding USB port multiplication, the big concern is the communication between the chipsets of the MB561U3S-4S R1 and the Synology. The MB561U3S-4S R1 uses JMicron JMS575 and JMS567. The JMS567 handles the SATA to USB connection and would place all 4 drive connections into the single USB connection. USB port multiplication is the ability to see multiple connections in a single USB physical connection. Desktop computers generally have this on their USB connections but NAS systems might not have this. The MB561U3S-4S R1 does not behave like a USB hub. Any changes in the physical connections while the unit is on, such as removing a hard drive would refresh the USB connection, affecting all drives that are inside the unit.
As for the fan, we do not have a decibel measurement on the fan used in the MB561U3S-4S R1. As for the differences between the MB561 models, previous models have a different internal design regarding the power supply along with older connection standards such as USB 2.0.
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