For raid5 on an array with more than 3 drive, if you attempt to write a single block, it will: - read the current value of the block, and the parity block. - "subtract" the old value of the block from the parity, and "add" the new value. - write out the new data and the new parity. If the parity was wrong before, it will still be wrong. If you then lose a drive, you lose your data.
Wow, that really needs to be put somewhere in 120 point red blinking text. A lot of us are used to uninitialized disks calculating the parity-on-first-write, but if linux MD is forgoeing that 'dangerous-no-resync' sounds really REALLY bad. How about at least a 'Warning: unlike other systems this WILL cause corruption if you forego reconstruction' on mkraid? - 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
