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RAID 1 - How to remove drive and see it has a normal hard drive?

Posted on 2013-01-02
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Last Modified: 2013-01-27
I have a RAID 1 with a failing hard drive (SMART Errors).  When I remove this hard drive how can I just connect it to a normal SATA port and access the drive like a normal hard drive.

I know that it will have the RAID metadata intact so it won't work as a normal drive.

What are the steps to remove the RAID metadata so that I can connect it to another node acting as just a normal hard drive (non-RAID)?
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Question by:bdeback
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by:dlethe
ID: 38738895
Get a binary editor and look for the partition headers, then boot to linux and use dd to image from the appropriate starting offset to another device.    That is free, but if you don't understand the process then best you go down another path.

Use something like runtime.org RAID reconstructor to do it.  Price is around $100
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by:teomcam
ID: 38738919
Since its RAID1, it will already act as normal HDD. Just plug it that's all.
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by:dlethe
ID: 38738936
Teomcam:   and how do you expect this to work when logical block zero is not the same as physical block zero?   There are N blocks of metadata starting at physical block #0.  (Let's say capacity is M blocks).  

One needs to shift M-N blocks at offset N to offset 0.  This can be done in-place by writing a shell script, a C program, or buying some software.  But it needs to be done where at least the target drive is behind a non-RAID controller
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by:brokenbyte
ID: 38738967
I think Teomcam may be referring to a software RAID1, such as something created within the OS. If that's the case, then I think you are able to move your HDDs around freely.

Given that you're talking about SMART errors, my guess is that you are using a hardware RAID controller, such as a Smart Array controller (HP).

Bdeback: can you give us some more information on what you are using to control the RAID?
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by:dlethe
ID: 38739191
If it is host-based/software RAID then then there is still metadata. One disk has to be primary, the other secondary.  Both HDDs will believe they are degraded volumes and that won't change w/o running some code.

If it is a "fakeraid" controller then it won't even boot.  But it is moot.  You end up with two degraded RAID sets, and if you are foolish to try to mount one of them then you turn that drive into a foreign disk, change the data, and you can't put the two disks back into a RAID1 set ... at least not w/o doing a full rebuild.
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by:rindi
ID: 38739208
Why are you trying to connect the drive that has the SMART errors to another PC? Just replace it with a good drive and allow the RAID to rebuild, and do this as soon as possible.
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noxcho earned 500 total points
ID: 38739298
Actually the purpose of Mirror RAID is to use one of the drives as single HDD in case the other one dies unexpectedly. And meta-data should not prevent accessing this drive.
Otherwise I don't see any use of RAID1 Mirror at all. And it is no difference there if software or hardware RAID is used. in case of hardware RAID the data is simply mirrored to both drives so they get exactly similar bit structure.
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by:dlethe
ID: 38825353
Respectfully, Noxcho - you are dead wrong on this.  HP SMARArray, 3WARE/AMCC; LSI MegaRAID; Adaptec; Dell PERC; all use metadata, and they are just a few off the top of my head because I have developer agreements on these controllers.

The metadata is used for a variety of reasons -- to insure the configuration doesn't get lost if the RAID controller dies;  to deal with situations where a drive fails or is partially through a rebuild and power is lost.

Even single-disk "JBOD" disks have metadata on some controllers, such as HP.

One can easily PROVE if metadata exists by looking at the usable block count on the resulting RAID1.  If it doesn't match the manufacturer's specs, then you know it must reserve something for metadata.

The metadata is also NOT mirrored, exactly, between all the disks in the set.
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