What's '' DISK FAILURE IS IMMINENT''?

[Yeshining]

After I install the ubuntu operation system,the ''Palimpsest Disk utility'' alert ''DISK FAILURE IS IMMINENT''
and when I click the link 'More information'
It shows as below:
Self Assessment: FAILING;
Overall Assessment:DISK FAILURE IS IMINENT Backup all data and replace the disk.
Attibutes:
5 reallocated sector count------failing


Please tell me more about the information and how to deal with the issue.

[sanz]

Backup all data and replace the disk.