Failed Redundancy (system, boot, page file, crash dump)

We started having backup problems using Windows Backup in MS SBS 2008 R2 HP Server. we re-booted and all was ok until Friday backup. We receiver the following error : "A volume Shadow copy service operation failed". Detail Error : " The volume Shadow copy operation failed with error 0x800423F4. I went into Disk Manager and checked the hard disk which is a Mirrored Raid. I notice that one of the volumes was not activated. When I tried to Reactivate I get the following pop-up box "The Plex is missing" I am very new to this stuff This job was passed down to me when company down sized we only have 5 user including me. : What is plex ? PLEASE HELP
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you can use this method :  
General troubleshooting
1.Check the event log for failure events logged by Windows Server Backup by opening the Event Viewer and review the logs: Windows Logs\Application where the source is Backup.
2.Identify which application or layer caused the issue. The event in the previous step will usually indicate which layer or application caused the failure. For example, where VSS is the cause, you may see the following message:
Check VSS event log for details
Check the event log for the problematic application reported in the failure event.
3.Analyze the events belonging to the application to understand the root cause. The events may point to issues in a different application. To do so, search for the events logged by the application found in step 2. For example, for errors caused by VSS, search for all events where the value in the Source column is VSS.
4.Repeat step 2 and step 3 until you get to the root cause of the problem and then correct the problem.

here an artticle about plex problems on server 2008
On Windows Built-in Software RAID "Plex" means one of the two physical disks that make the array. If one of the "Plex" is down, that is usually because one of the disks has failed, and then you shouldn't just reactivate the volume, as trying to add a bad disk to an array again will cause issues.

You should rather first of all make sure your backup is up-to-date. As in your case it has failed, I suggest making an offline backup using a 3rd party tool which you boot from first. CloneZilla is OpenSource and free and very good for that:

Once the backup is done, find out which disk is bad. Best use the disk manufacturer's diagnostic tool for that. Most of them are included on the UBCD:

Once you have the bad disk, replace it with a good new one. After that rebuilt the array.

Also run a chkdsk /r /f on all drive letters to fix ntfs file-system corruptions. Those are likely to have caused the problems with VSS.
noxchoGlobal Support CoordinatorCommented:
Replace the failed drive. And then re-mirror the healthy drive with it.

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PoppygbAuthor Commented:
You guys rock
if i had a rocking chair, yes
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