Wrong. If you have eight drives in JBOD, and one of them dies, there are several options:
- On NTFS filesystem, if first drive dies, the entire array is lost. If any other drive dies, 7/8th of the data is lost.
- On ext-whatever, you can salvage an unspecified amount of data because the superblocks are distributed more-or-less evenly across the volume. However, everything in disk groups which span across two disks is likely lost. So you can theoretically approach "1/8th of the data lost", but that involves using some data recovery software and is far from easy.
If you want to be sure that the loss is limited to 1/8th of data in eight-disk configuration, forget JBOD and create eight separate volumes instead.