You are very welcome.
ETH0, ETH1 are the ports where iSCSI data goes to and from the switches. So that's how your servers get to the SAN storage. Via those two ports. Without both you can hinder performance and lose redundancy. It is important that you resolve this issue soon. You can upgrade with just one active iSCSI port.
I am planning to upgrade live SAN, Can we take any backup/snapshots and store it for safety. Currently we dont have replication or backups in place. Actually we don’t have much storage space, can we store backups anywhere in cloud. If so can you please let us know how to take it.
Are you referring to the data on the SAN, or the SAN configuration metadata? If you are talking about your actual data, there's no direct from SAN-to-Cloud backup option. You can of course purchase storage cloud storage then via your hosts back up the data to the cloud.
There are hosting companies that will provide you with EqualLogic based replication storage partner so you can utilize the replication feature built into the array. Depending on how much data you have and your Internet bandwidth that could take sometime to get the data copied. After that it will only be the changes.
How much data is on the array? It might be cheaper and faster to purchase 15TB external hard drives and backup your data to those. Then going forward you have a way to backup your data.
Firmware updates by themselves don't pose a risk to your data. The process used is the same as if you had a controller failure. The update doesn't write to your data, it updates the code on the compact flash cards on each controller. All your data and array configuration, logs, etc are stored on the array disks themselves. Never on a controller.