On Sun, Mar 7, 2010 at 4:52 AM, Goswin von Brederlow <goswin-v-b@xxxxxx> wrote: > Neil Brown <neilb@xxxxxxx> writes: > >> On Sat, 06 Mar 2010 18:17:44 -0500 >> "Guy Watkins" <linux-raid@xxxxxxxxxxxxxxxx> wrote: >> >>> } >>> } At a minimum I would build a 3-disk raid 6. raid 6 does a lot of i/o >>> } which may be a problem. >>> >>> If he only needs 3 drives I would recommend RAID1. Can still loose 2 drives >>> and you don't have the RAID6 I/O overhead. >>> >> >> and as md/raid6 requires at least 4 drives, RAID1 is not just the best >> solution to survive two failures on a 3-device array, it is the only solution. >> >> NeilBrown > > Except that there also is raid10 with 3 mirrors. :) > > MfG > Goswin > > PS: Why doesn't raid6 still not allow 3 drives for the special case of > converting raid1 -> raid6? > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > That should be obvious: Possible stripes: Start: 1, 1, 1; 2, 2, 2; 'raid6' overtake... 1, q, Q; 2, q, Q; 'raid6' overtake with missing; 1, (missing 2), q, Q; 3, (missing 4), q, Q; In the first overtake case you have the requirement of generating 200% parity, which probably won't work for the algorithm and is a silly idea in general since it's computationally far less expensive to store another copy of either form of data instead. In the second you're gaining the space of a second disk at the cost of being already degraded; why not just go for raid 5 instead? You can overtake raid5 later with raid6 if you add more devices. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
