Checksum Transfer Size and Delta Block Transfer Size have nothing to do with the size of the chunks of a file that we calculate checksums against. By default, PeerGFS creates checksums (64-byte MD4 checksums) for each block that range between 8 KB and 1 MB. The algorithm auto-adjusts based on the nature of the file in question. This setting is not and has never been configurable from the PeerGFS user interface.
Changing Checksum Transfer Size actually impacts the number of checksums that we send from target to source in one shot. Think of this like a buffer for checksum values. PeerGFS calculates a checksum for each block of a target file and sticks the checksum into a 256 KB buffer. If the buffer becomes full, we'll send it to the source and put the remaining checksum values into another. If all checksums for a file do not fill a single buffer, we'll send the buffer only partially full. The checksums for most files will fit within the default 256 KB.
Changing Delta Block Transfer Size actually impacts the number of bytes of file differences that we send from source to target in one shot. Again, think of this like a buffer. For each checksum comparison, the source Agent will put either an "in-sync" flag or the actual 8 KB of the source file that needs to be sent to the target into the buffer. When the buffer becomes full, we'll send it to the target and begin to fill another.
Note: Both of these settings affect single file delta compression logic only. Partially empty buffers are not shared across files, but rather sent when delta compression logic for a single file is complete.
The only time we recommend increasing these values is when you have many large files >100 MB in size. Increasing these values can help optimize delta compression performance but it impacts memory usage by all Agents. I f you do decide to increase one of these values, the best practice is to always increase BOTH values at the same time and with the same increments. We currently do NOT recommend ever lowering them.