Appendix B - Recovering From Power Failures and Disk Overloads
Recovering from Power Failures
How your server recovers from a power failure depends on whether you have a battery backup installed. This section explains how to recover from a power failure whether or not a battery backup exists.
Power Failures with No Battery Backup
If the line power to the server drops below a usable level, the system performs a fast shutdown. When no battery backup exists, the server does not have time to flush written disk blocks to disk. The system ensures only that no errors are written to the disk.
Users who attempt to access the server while it is shut down receive warning messages that the server is unavailable.
When power is restored, the server automatically reboots and performs a complete check on the system disks. If incomplete disk structures are detected, the problems are corrected automatically. Users may experience some data loss in the files that they were writing to disk when the power failure occurred.
When all services are running, users should be able to continue their work without interruption. If a user was in the process of writing to a server disk, the user should examine the data to verify its correctness before continuing. If a workstation does not recover properly, the user must reboot the workstation.
Power Failures with Battery Backup
If the line power to the server drops below a usable level, the server switches to battery power and starts a proper shutdown of the system. During the shutdown, the system ensures that all data on the server's disks is secure. Users who attempt to access the server while it is shut down receive warning messages at the workstation that the server is unavailable.
When the line power is restored, the server reboots automatically. Once all services are running, users should be able to continue their work without intervention. If a workstation does not recover properly, the user should reboot the workstation.
When disk1 fills up, the following message appears on the server console:
Out of disk space on hard disk device n, drive n
The server does not immediately crash if disk1 is full. Instead, the server stays running long enough for you to delete data from disk1 (such as removing the mail service). The length of time depends on the amount and kind of current network activity. If you do not remove files from disk1, the server eventually halts, due to a lack of available disk space.
Even if some services (StreetTalk, Mail, and so on) become inoperative, you are able to delete data from disk1.
As an alternative, you have the ability to restore data from your last backup, which can get the server up and running again. Note that you will lose any data created after the last backup but before the disk filled up.