On Sunday February 17, beolach@xxxxxxxxx wrote: > On Sun, 17 Feb 2008 14:31:22 +0100 > Janek Kozicki <janek_listy@xxxxx> wrote: > > > oh, right - Sevrin Robstad has a good idea to solve your problem - > > create raid6 with one missing member. And add this member, when you > > have it, next year or such. > > > > I thought I read that would involve a huge performance hit, since > then everything would require parity calculations. Or would that > just be w/ 2 missing drives? A raid6 with one missing drive would have a little bit of a performance hit over raid5. Partly there is a CPU hit to calculate the Q block which is slower than calculating normal parity. Partly there is the fact that raid6 never does "read-modify-write" cycles, so to update one block in a stripe, it has to read all the other data blocks. But the worst aspect of doing this that if you have a system crash, you could get hidden data corruption. After a system crash you cannot trust parity data (as it may have been in the process of being updated) so you have to regenerate it from known good data. But if your array is degraded, you don't have all the known good data, so you loose. It is really best to avoid degraded raid4/5/6 arrays when at all possible. NeilBrown - 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
