We're talking about btrfs raid1 here which always gives you half of total capacity of all disks (except for extreme cases). With 5 drives it's 2.5 drive worth o

We're talking about btrfs raid1 here which always gives you half of total capacity of all disks (except for extreme cases). With 5 drives it's 2.5 drive worth of data. If 2 drives die means 1 drive worth of data was lost (more or less, depends on balance).