Every hard disk has bad blocks and reserve space of good blocks to allocate from when one of these bad blocks is written upon. Also the drive's firmware has an

Every hard disk has bad blocks and reserve space of good blocks to allocate from when one of these bad blocks is written upon. Also the drive's firmware has an internal list of known bad blocks discovered while a low level format was performed at the factory, which is why consumers should not perform a low level format ever again, unless they are aware of this and know how to write the updated bad blocks list back into the drive. Either way, bad blocks on a hard disk are an unavoidable reality. The same is true for SSD's. It is normal and should be expected to run into bad blocks on the media during normal use of the hard drive, whereby the correctly programmed firmware will remap the pointer to a good block from the reserve and either tell the OS driver to attempt the write again (if the drive's write cache has been disabled, as it should be), or silently re-map to the good block and write it with the data from the drive's write cache. If power is lost during this, no amount of redundancy will save one. The only solution is ZFS or Oracle ASM. It has always been this way, and will always be like this as long as we don't have media which cannot have bad "blocks", for lack of a better term.