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.
Best Answer
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.