[CentOS] SMART Prefailure Attribute messages

Hello,
My machine is running Software RAID 5 on /dev/hde1, /dev/hdg1,/dev/hdi1. I 
noticed on the log that suddenly we are getting messages such as : 

Oct 14 01:27:16 localhost smartd[4801]: Device: /dev/hde, SMART Prefailure 
Attribute: 8 Seek_Time_Performance changed from 247 to 246 
Oct 14 01:57:15 localhost smartd[4801]: Device: /dev/hde, SMART Prefailure 
Attribute: 8 Seek_Time_Performance changed from 246 to 245 
Oct 14 02:27:15 localhost smartd[4801]: Device: /dev/hde, SMART Prefailure 
Attribute: 8 Seek_Time_Performance changed from 245 to 246 
Oct 14 02:27:15 localhost smartd[4801]: Device: /dev/hde, SMART Usage 
Attribute: 195 Hardware_ECC_Recovered changed from 253 to 252 
Oct 14 02:57:15 localhost smartd[4801]: Device: /dev/hde, SMART Prefailure 
Attribute: 8 Seek_Time_Performance changed from 246 to 245 
Oct 14 02:57:15 localhost smartd[4801]: Device: /dev/hde, SMART Usage 
Attribute: 195 Hardware_ECC_Recovered changed from 252 to 253 

Similar messages for /dev/hdi and /dev/hdg also, however it seems 
that /dev/hde has the most and have been occuring the longest. 

[root at localhost log]# grep SMART messages messages.1 | grep hde | wc
    178    3023   25944
[root at localhost log]# grep SMART messages messages.1 | grep hdg | wc
     93    1578   13583
[root at localhost log]# grep SMART messages messages.1 | grep hdi | wc
     95    1612   13865

This did not happen a week ago: 
[root at pathfinder log]# grep SMART messages.2 

Checking /proc/mdstat indicates that all the drives are active i.e. RAID is 
not running in degraded mode. 

So, is it that suddenly my drives are failing ? 
Any comment or suggestion is greatly appreciated.

Thanks.
RDB
-- 
Reuben D. Budiardja
Department of Physics and Astronomy
The University of Tennessee, Knoxville, TN