> afaikt, MD raid1 assumes that any data-corrupting errors are reported. > if the device corrupts data and lies to the driver/kernel/md, then you > are in trouble. this applies to both reads and writes. > > it's easy to imagine a ckraid1 tool that somehow forces reads of all > copies of each block. but with two mirrors, there would presumably > be no way to decide which to use... > > all that said, I've never seen this happen. Unfortunately, I've seen things like this not just but quite a few times: Sometimes it seems to happen that over time sectors on a harddisk can become unreadable. As long as you don't actually access that sector there's no way to detect this kind of failure. Later, either a read/write error or an unclean shutdown causes the OTHER disk to be kicked out of a raid array. Now, during resync, the bad sector is noticed and causes the resync to fail. Recovery from this situation is fairly aggravating. A chraid functuon / tool would greatly help by detecting faild / bad sectors while there still is a good copy of those sectors available. > then again, raid1 is a sort of ugly niche feature, IMO. how many > systems can afford two but not three disks? raid5 is not scary! Urr, I don't agree at all here: If you've got lots of small random writes (in practice: a database) raid 5 performance really sucks, raid1 is much better here. Also, 3 disks may not be physically feasible in all configurations. Bye, Martin - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
