RAID terminology

Here is a question I have been scratching my head over lately.  What does synchronizing an array mean?

Background information:
This specifically pertains to an ASUS A8N32-SLI Deluxe motherboard using the nVidia RAID controller with 4 400GB HDs in RAID 5.  There are two options in MediaShield (the software to manage the RAID controller in Windows) regarding RAID5, rebuild and synchronize, among others.  Rebuild seems rather obvious, when a faulty drive is replaced the data is rebuilt onto the new drive.  Rebuilding is relatively fast, compared to synchronizing which seems to take over 24 hours to complete.

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CallandorConnect With a Mentor Commented:
According to the nVidia manual, synchronizing an array forces a rebuild of parity, which applies to RAID1, 0+1, and RAID 5.  Rebuild uses the existing parity to reconstruct missing data.
jdietrichConnect With a Mentor Commented:
You don't really synchronize a RAID 5 array.  Synchronizing is used in mirroring.  When you have 2 drives (or more) mirrored, depending on the controller you can chedule synchorizing, which goes out and checks to array to ensure that it is an exact mirrored copy.  I run these nightly in some places.  It will generate a log telling me no issues or that there were issues, which in that case if I see a pattern usually tells me the controller or a drive is starting to fail.  Some advanced controllers that support RAID V also do something similar, which is a parity check.  It is possible that is what they are referring to.  Like a synchronize, the controller will check the drives to ensure the parity is in sync so that any of the drives can be rebuilt by the three others.  I know the term as parity check, they are more than likely applying it to this...
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