ScSI raid failure question

I have a server that has a raid card with 2 channels.  channel 1 is mirrored, raid 1.  Channel 2 is raid 5 with 4 drives.

2 of the drives failed in the raid 5 and ofcourse shut down the raid.

I have 2 drives on the way for replacement but I wanted to know.

I can force 1 of the drives online and it comes back up, when I try to force the second one to rebuild it fails again.  

but if I force 1 online will that be enough to get things running again?  I can replace the 4th drive and rebuild.

I wasn't sure what would happen if I force the 3rd drive online if the raid would start to work after a reboot.

and for replacing the drives.  what would be the best pratice for replacing 2 drives?  just replace them both, force them online and rebuild?

thanks
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lefty431Asked:
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wjesterCommented:
Since it's RAID 5 you can only have 1 failed drive. If you can force 1 of the failed drives back online you should be okay. When the replacements come, replace the failed drive first and then rebuild. After the rebuild is complete, replace the failed drive that you forced online and rebuild again.
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lefty431Author Commented:
ok.  one other thing.  what happens if you have 2 36gig drives and they don't make them anymore.  can you use a larger drive?  have 1 36 gig and 1 146 gig?  it is ok if the raid card anly uses 36 but just checking if it is possable.  

also, by just forcing one of the drives online, does the system start to update the data on it without rebuilding?
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lefty431Author Commented:
why can't I just force both drives online without rebuilding?? I guess that is the real questioin.  It looks like Power Console gives me that option, but I don't want to break anything.  
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wjesterCommented:
yes, you can replace a smaller drive with a larger drive. you'll just lose the space that is greater than the size of the original smaller drive (well, you can actually still access it, just as a separate logical drive).

how badly the drive is damaged will determine whether or not you can force it online. either way, you're going to need to replace both. when you force one of the drives online, a rebuild doesn't occur. the controller just uses the parity information stored on the "live" drives to replace what is missing on the "dead" drive. the rebuild will only occur when all elements are back online.
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andyalderCommented:
Assuming the disks didn't both fail at exactly the same time you should force the one that failed most recently back online and then backup, then erase the other disk and let it rebuild. When you force the second disk online it is not in sync with the other three and so kills it.

Forcing the disk with the older data online should also lead to a completely corrupt system since they aren't the same date but the correct disk is at the correct date since when it failed the system stopped dead. At worst you just get the equivalent of powering off the server while it was running which chkdsk can normally fix.
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Computer101Commented:
Forced accept.

Computer101
EE Admin
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lefty431Author Commented:
sorry.  what is accepted is fine.
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