# mdadm RAID-1: Are the partitions identical?

## ShyGuy91284

I would like to make a backup of my system, which contains a couple RAID-1 arrays on three drives.  My question is, are the RAID-1 partitions identical (assuming I made sure they were synchronized before shutdown)?  Can I back up one partition, and restore it to all three drives in the event of a failure and it will work right?  

Thanks in advance.

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## Mad Merlin

I would suggest you not go around your RAID array. Tar up the filesystem on top of it, not the raw bytes underneath.

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## ShyGuy91284

Yeah, that's what I am doing.  When I boot up a liveCD though, it detects the RAID elements as seperate drives.  I'm wondering if they are identical so I know if I need to tar up one drive for many, or each drive individually.

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## BradN

The data stored within each raid partition are identical with RAID-1; that's the definition of RAID-1.  However, the metadata will be different so it can identify which raid device a particular disk is.  That said, you can get by with only backing up one of the raw drives, since RAID-1 will run if only one is present (ie, in a recovery situation), and you can just add a new blank raid device to replace the other one.

If the volume is very full, it could be considerably faster to back up the raw device than the contents.

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## nielchiano

Just to note that you need to watch out when recovering. You'll probabely restore the tar onto a single disk, and re-sync the RAID. Make sure that the RAID chooses the "right" drive to start from...

 *BradN wrote:*   

> That said, you can get by with only backing up one of the raw drives, since RAID-1 will run if only one is present (ie, in a recovery situation), and you can just add a new blank raid device to replace the other one.

 

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## BradN

Right - create the new array with only the working drive present (use the missing keyword for the other one), then add the blank one.

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