The memory for Ethernet adapter on rack 89 on fanuc robot controller is limitted.

For 30iB controller, maximum number of input bytes per connection (ccombination of Digital and Analog) is 248 Words or 496 Bytes. This is the maximum you can use on Ethernet. Which means, this includes your PLC and other devices you may have other than the IO Block you mentioned. For 30iA, it is even lesser.

And, the IO Link blocks use crazy amount of memeory. Balluff has new blocks with hardware version 9. These has the ability to configure how many byt to be used for IO Link ports rather than the standard 32 bytes memory allocation.

But I am not using all 8 ports, I am using only 5.

It doesnt matter. Once you add the IO Block in the Ethernet/IP page on the teach pendant, you have to input the actual size of input and output of the IO Block. That will reserve the memory. Then you can map whatever bits of data from the stack to DIs or DOs.