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Old 04-07-2006, 02:02 PM   #1
Registered: Jun 2004
Posts: 124

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RAID-1 to RAID-5 Migration?

My current setup is 2x250gb RAID-1, however, its filling up _very_ rapidly, and needs to be upgraded. I have another 250gb drive spare, and would like to migrate to a 3x250gb RAID-5. Like I said, I'm working with a limited number of drives (3x250gb), so backing up is somewhat out of the question.

I've heard I can do the following:
Remove one of the drives from my current RAID1, and just make it a degraded RAID1 (still running, just like if a drive had died).
Using the other two 250s (one that was removed, and the spare), create a degraded 3-disk RAID5 array.
Copy everything from the degraded RAID1 to the degraded RAID5.
:: ensure everything copies successfully ::
Delete the RAID1 array
Hot-Add the last 250 to the runnin RAID5.

While this seems like a perfectly logical solution (Both RAID1 and RAID5 are built to run with successfully while missing a disk), it seems slightly dangerous.

I'm using mdadm, but can't seem to find anything online about creating a degraded to start with RAID5. Can anyone help me out? Has anyone done this? (Maybe a snippet of shell code for creating a degraded RAID5?)
Old 04-08-2006, 11:13 PM   #2
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You can create a degraded array by using the word "missing" in place of the device when creating the array (this is from the mdadm man page, I've never tried it). Then you could add a device later with --add.

This is slightly dangerous. If you're remaining RAID-1 drive fails when you're copying from the degraded RAID-1 to the degraded RAID-5 or one of the RAID-5 drives fails while the array is rebuilding after the addition of the new drive, you could lose some or all of your data. It's up to you to decide whether it's worth it.
Old 04-09-2006, 12:21 AM   #3
Registered: Jun 2004
Posts: 124

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The only time there would be data-loss however would be if one of the three drives died while in the process of degrading/copying/rebuilding, correct? Assuming a drive doesn't die in the middle, the plan is a logical way of doing it?


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