For some reasons it is necessarry to enable circular logging on your Exchange databases.
This reasons could be moving many or large mailboxes or perhaps a broken backup which causes the logfile partition to be stuffed with logfiles.
However, you can enable circular logging via Exchange Management Console (EMC) or via PowerShell. With PowerShell you can set it for all databases at once.
Get-Mailboxdatabase | Set-MailboxDatabase -CircularloggingEnabled:$true
I would strongly suggest enabling circular logging should be the last option. After you solve your issue you should immidiately disable circular logging.
Get-Mailboxdatabase | Set-MailboxDatabase -CircularloggingEnabled:$false