I have a 5TB, 2 collection instance that I need to move from zlib to zstd. The initial sync is painfully slow right now on a very beefy secondary instance (m5.12xlarge, 192GB of RAM, 48vCPUs). The initial sync is scheduled to be completed in 8 days.
Primary instance is on an even beefier machine with no load. I tried diagnosing the slowdown and determined
disk is not saturated with iostat
cpu is not saturated with htop.
changing instance type to increase/decrease RAM
played around with maxIndexBuildMemoryUsageMegabytes with setParameter
played around with replWriterThreadCount with setParameter
It seems like the instance can do a lot more with disk + CPU not saturated on both the primary and the secondary. Is there anything else I can try?