How many resources does the Esxi host have and how many is it consuming?
The first thing I would do is restart the Esxi host.
5.5 has been out of support for a while, and 6.0 goes that way very soon too - definitely upgrade if you can (regardless of your current issue)
thanks for the answer
my server have many resources. have 48 GB ram and CPU 32 cores.
when i tried to reboot after the issue continue, so i think that no os the problem.
So in this moment i migrate my vms more importants to another host an works perfect but, i dont know where star to invesigate because the logs dont show some important.
Run this test, migrate all the virtual machines to another host, then move them one at a time and verify that it is working properly.
If it works, migrate another VM and test the functionality again ... keep it up and see the result.
How much Ram do each VM have?
each Vm have diferentes memory ram assigned
But all the vms does not exceed physical memory
1. How the VMs are provisioned? Is it thin or thick provision?
2. What is NAS? Is it a single iSCSI LUN connected? What is the RAID level? What are its settings? Have you tweaked networking between NAS and VMware host?