This would seem to be indicating that the syncing between the 2 members of the RAID are not staying in sync with each other.
1. Investigate logs
I'd investigate your
dmesg logs and see if there are any messages stating that either of the physical HDDs that make up this array are having hardware failures.
2. Check mdadm
You can also consult
mdadm using the
--detail switch to find out more information about the resync like so:
$ sudo mdadm --detail /dev/md0
Version : 00.90.03
Creation Time : Sat Jan 26 09:14:11 2008
Raid Level : raid1
Array Size : 976759936 (931.51 GiB 1000.20 GB)
Used Dev Size : 976759936 (931.51 GiB 1000.20 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Fri Jan 1 01:29:16 2010
State : clean, resyncing
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Rebuild Status : 50% complete
UUID : 37a3bfcb:41393031:23c133e6:3b879f08
Events : 0.2178969
Number Major Minor RaidDevice State
0 8 1 0 active sync /dev/sda1
1 8 17 1 active sync /dev/sdb1
If both devices seem fine and you cannot pinpoint which device is having an issue, you may want to temporarily run a diagnostic tool such as HDAT2 or SpinRite against each HDD to confirm their health.
If the HDDs check out then I would start scrutinizing the cabling, I typically will swap these out.
I'd next scrutinize the controller itself, either taking the drives out of the affected system and diagnose them in a secondary system, or add a 3rd party controller card into the affected system to diagnose the issue further.
5. Power supply
Believe it or not, I've had issues in the past with HDDs and RAIDs where swapping out a failing, or about to fail, power supply, resolved my RAID health issues.