It's a very different architecture. 3FS is storing everything on SSDs, which makes it extremely expensive but also low latency (think ~100-300us for access). JuiceFS stores data in S3, which is extremely cheap but very high latency (~20-60ms for access). The performance scalability should be pretty similar, if you're able to tolerate the latency numbers. Of course, they both use databases for the metadata layer, so assuming you pick the same one -- the metadata performance should also be similar.