Yeah, I had try some cases to solve my problem, include set each shards to the tens of GB in size. I found that:
in my case, one shard with 70GB in size, the shard may cost about 470 MB term_memory.
So if I used all of 32GB RAM, means that I can store about 32GB/470MB=68 shards. 68
shards can only store 70GB*68=4.7TB
