Upgrading or downgrading Arista switch software is accomplished by replacing the EOS image and reloading the switch. Depending on the switch model and the software change being made, there are different options for minimizing (or potentially eliminating) downtime and packet loss during the upgrade/downgrade.
Accelerated Software Upgrade (ASU) :ASU is available on the 7050SX-64, 7050SX-128, 7050Q-32, and 7050Q-32S and can be used on both leaf and spine switches. It significantly reduces reload time by streamlining and optimizing the reload procedure for upgrades, and continues sending LACP PDUs while the CPU is rebooting, keeping port channels operational during the reload. Downtime during the upgrade is reduced to 30 seconds. Note: ASU does not support software downgrades.
Leaf Smart System Upgrade (Leaf SSU) :SSU is available only on 7050X platforms (excluding 7050SX-72 and 7050SX-96), and can only be used on leaf switches. It includes the core functionality of ASU, plus additional elements that permit a hitless restart of several features. SSU does not support software downgrades, and is incompatible with VRRP.
Standard Upgrades and Downgrades :In those cases where an accelerated upgrade is not an option (such as software downgrades and unsupported platforms), performing a standard upgrade or downgrade using the steps described here will minimize downtime and packet loss.