[Bug] [broker]Disk iops cannot be higher than 4k，seems to be affected by Direct I/O

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Version

3 Aliyun ecs，broker and bookie share a disk
disk have 16800 iops
pulsar-version：3.0.0
CentOS Linux release 7.9.2009 (Core)
3.10.0-1160.88.1.el7.x86_64

### Minimal reproduce step

Through the fni tool, when testing disk performance, it is found that turning on/off direct has a great impact on disk iops

### What did you expect to see?

I hope to see that the disk io of pulsar can exceed 4k

### What did you see instead?


### Anything else?

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start by reproducing the reported disk I/O behavior on Pulsar 3.0.0 with the broker and bookie sharing an Aliyun ECS disk, comparing direct I/O enabled and disabled. Check the broker and bookie disk-I/O paths to identify why throughput appears capped near 4k, then verify the result with the same disk-performance test.

Written by the indexing model from the issue text.