Replication delay when Durability Level is set to Majority and persist to active

I am running a server with Durability Level set to “Majority and persist to active”.
After about a month, replication is delayed and response is slow.
I have tried changing various kernel parameters, but there seems to be no change.
If there are any points that should be reviewed, please let us know.

The configuration of the target server is as follows.

CPU:AMD EPYC 7J13 64-Core Processor 4Core8Thread
OS:Oracle Linux 7.8(4.14.35-1902.303.4.1.el7uek.x86_64)

$ cat /etc/sysctl.conf
fs.aio-max-nr = 1048576
kernel.sem = 250 32000 100 128
net.core.rmem_default = 262144
net.core.rmem_max = 16777216
net.core.netdev_max_backlog = 30000
net.core.rps_sock_flow_entries = 32768
net.core.somaxconn = 32768
net.core.wmem_default = 262144
net.core.wmem_max = 16777216
net.ipv4.ip_local_port_range = 1024 65500
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
vm.swappiness = 0
vm.dirty_background_ratio = 1
vm.dirty_ratio = 3
vm.vfs_cache_pressure = 50
vm.min_free_kbytes = 524288

Version:Community Edition 6.6.0 build 7909
Service:Only “data” is valid
Memory Quotas:21504MB
Reader Thread Settings:Disk i/o optimized
Writer Thread Settings:Disk i/o optimized
number of buckets:1
Server Nodes:4
Item count:about 20,000,000

Since it is possible that the machine translation may not have conveyed the message well, the original text (in Japanese) is also included below.

運用しているサーバーでDurability Levelを「Majority and persist to active」にして動かしているのですが、

Apologies for the delay here. Are you still seeing this behavior in Couchbase 7.x? We had made many improvements to the durability performance since 6.6

Thank you for your reply.

We are not currently planning a version bump for Couchbase7.x.

We had made many improvements to the durability performance since 6.6

I received your answer, but has this change been reflected in 6.6.x?

Best Regard,

No, that’s what I was saying. We have made many improvements in versions after 6.6.

You may also want to consider testing your behavior with our new storage engine, Magma which provides much better performance when writing to disk: Magma: The Next-Generation Document Storage Engine

I understand the upgrade.
I would like to consider this.
Thank you very much for taking time out of your busy schedule to reply.