Putting aside the costs and laboriousness associated with maintaining a local server, storage and assuring the backups are successful, we recommend your team address the following relevant questions in order to determine whether they can rely on this approach for backup and restore:
How frequently is the data pulled from Salesforce?
How frequently is the local database backed up? What is the retention policy of those local backups?
Does your local database include your Salesforce.com attachments?
Does your backup include your Salesforce.com Metadata (e.g., Reports, Layouts, AppexCode, Workflows, Dashboards, etc.)?
How would you restore from a user-inflicted Salesforce data loss scenario? Would a potential Salesforce data corruption or deletion propagate to your local database (thus corrupting the local database)?
If so, would the restore process then involve an additional step of first restoring a good snapshot from the backup to the local database before ultimately restoring from the local database to a Salesforce Org?
How long will it take to complete this two-phase restore procedure?
Can you easily practice your DR procedure? Does your local database include a sandbox environment for DR testing purposes?
Sometimes you just want to talk to someone. Our customer support team is available by phone: