I found that the data transfer of Omicron triggers files is very slow. I doubted this problem due to disk access on k1sum1. So I replace this HDD with the SSD and the transfer speed is improved.
I found that the one data transfer of Omicron triggers took about 5hours. This is taking too long because data transfer is set to occur once every 30 minutes.
At first, I thought that NFS might be the cause. I increased the number of NFS processes to 64 without much improvement.
Next, I stopped the frequent Omicron triggers writing. There was no significant speed increase, but there was some improvement.
Finally, the disk to which Omicron triggers have been written was changed from HDD to SSD. This has resulted in a dramatic improvement. Perhaps there are two effects: the elimination of extra files and the improved random access provided by the SSD.
While doing this work, I noticed that some servers were using bad LAN cables. So I replaced them.