Salesforce Upgrades and Maintenance

Salesforce reserves up to five minutes of service interuption for major upgrades, but you have access your data during other maintenance events, like splits and migrations.

• Read-Only Mode
  Access to your data at a moment’s notice—even during our planned maintenance windows. To minimize interruption to your business, Salesforce gives users read-only access during splits, instance migrations, instance switches, pre-scripts, and certain other maintenance events.
• 5 Minute Upgrades
  Salesforce reserves just five minutes of scheduled maintenance time to roll out new major versions of our service. These upgrades to the next release occur three times per year.
• Check for Desktop Client Updates
  Desktop clients such as Salesforce for Outlook and Connect Offline integrate Salesforce with your PC. Your administrator controls which desktop clients you are allowed to install.