Anybody who has had to replace a drive in a RAID array knows that the rebuild process can be long and painful. While all of that data is being copied, the array runs slowly and does not provide the usual protections. The advantage of running RAID within Btrfs is that the filesystem knows which blocks contain useful data and which do not. So, while an MD-based RAID array must copy an entire drive's worth of data, Btrfs can get by without copying unused blocks.
Isn't this something that could be achieved in an ordinary RAID if filesystems supported the TRIM feature that has been touted for SSDs?
Does anyone know if this is being worked on?
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