iSCSI storage performance drops after firewall rule changes – anyone else?

[mohsin045]

Now we're seeing random performance drops on the iSCSI connections – latency spikes, occasional timeouts. The VMs are still running but storage performance is inconsistent.
What we've checked:

• iSCSI network is on a separate VLAN
• Firewall rules are allowing all traffic on that VLAN (no restrictions)
• Jumbo frames are still enabled
• No changes to switch config

What we're seeing:

• Latency jumps from 1ms to 100ms+ randomly
• iSCSI session resets during high IO
• No errors in syslog that point to a clear cause

We're working with Syniix on some new storage hardware, and they're helping us debug, but we wanted to check if anyone here has seen similar issues.

Questions:

1. Could the firewall changes have affected something else indirectly (like MTU)?
2. Are there specific Proxmox settings we should check after firewall updates?
3. Any recommended tools for deeper iSCSI diagnostics?

Appreciate any suggestions.

 

[JohnnieKF]

Which firewall changed? The Proxmox host firewall, or an external appliance?