With minimum ISR set to 1, your cluster can have only a single broker with the data at any time, so if the disk of this broker was to blow up, you risk losing data.
If you want stronger guarantees, you need to increase the minimum ISR size. For example, if you set it to 2, at any time at least 2 brokers will have all the data. So in order to lose data in this configuration, you would need to lose the disks of both brokers within the same time frame which is a lot less likely than just losing a single disk.
If you increase minimum ISR, to ease maintenance, you probably also want to bump up the number of replicas so you can have 1 broker down and still be able to produce with acks = all.
Since you have replication factor as 2. Having 1 ISR out of two is sufficient. It means that Even if the leader goes down you have 1 replica to handle the transactions. Having more replicas will lead to higher write overhead and might slow down the throughput. You can have higher number of replicas at the cost of performance for reliability.
Similar question has been answered here :How does kafka handle network partitions?
In your case, I think there is no problem when network partitioning. Since unclean.leader.election.enable is false, one of two side cannot elect new leader so only the other side can accept write.
