Quote:

Why, though? Can't it just treat the sector contents as undefined until written to? Why isn't setup of an empty array instantaneous?


(following is edited from a message from Neil Brown - this comes up in the list a fair bit).

There is an --assume-clean option which is safe for raid1 and raid6 but for raid5 it is NOT safe to skip the initial sync. It is possible for all updates to be "read-modify-write" updates which assume the parity is correct. If it is wrong, it stays wrong. Then when you lose a drive, the parity blocks are wrong so the data you recover using them is wrong.
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LittleBlueThing Running twin 30's