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I've got a RAID1 array. I'm buying 4 more disks of equal size (they're the same model drives) and I'm trying to enumerate my options for a safe upgrade. Ideally they'll be one large ext3 volume.

Firstly, am I crazy? Do I really want to move software RAID1 to 5 or 6? Will I wish I never had? The machine is fairly powerful (an i7 with 12gigs of RAM) but will performance be significantly worse? Is R6 worse than R5?

I should add that there is nothing "running" of this disk - it's purely storage for a small network.

Step two: How do I do it? If I'm going for RAID6, is it best to create a new 6-disk RAID6 array in a failed state (ie 2 drives missing), copy the data across from the RAID1, break the RAID1 and add those disks to the RAID6?

I'm really keen for any feedback from mdadm users.

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up vote 7 down vote accepted

First, take backups.

Second, test backups.

Third, still sure? Take another backup.

Starting a raid 6 with 2 failed drives is not something to do lightly. Rebuilding the array is going to cause a lot of strain on those disks. One bad read, and all your data is gone. This is why people now recommend R6 and not R5, especially with TB drives: more reliability during rebuilds.

Performance wise, R5/6 should be fast for reads, may be slower for writes, although you go from a 2-disk setup to a 5-disk setup, so all bets are off.

In my opinion, the best way is to make a new RAID6 setup with all the disks, copy over and have two spare disks left (from the RAID 1).

Anyway, you should still make backups first.

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Did we mention backups? – bobby Aug 11 '11 at 20:33

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