Disk Partitions and Backups 229frequently tripling or quadrupling the tape used for backups. Another addi-
tional cost of running a Unix system.
Partitions: Twice the Fun
Because of Unix’s tendency to trash its own file system, early Unix gurus
developed a workaround to keep some of their files from getting regularly
trashed: partition the disk into separate spaces. If the system crashes, and
you get lucky, only half your data will be gone.
The file system gets trashed because the free list on disk is usually incon-
sistent. When Unix crashes, the disks with the most activity get the most
corrupted, because those are the most inconsistent disks—that is, they had
the greatest amount of information in memory and not on the disk. The
gurus decided to partition the disks instead, dividing a single physical disk
into several, smaller, virtual disks, each with its own file system.
The rational behind disk partitions is to keep enough of the operating sys-
tem intact after a system crash (a routine occurrence) to ensure a reboot
(after which the file system is repaired). By the same reasoning, it was bet-
ter to have a crashing Unix corrupt a user’s files than the operating system,
since you needed the operating system for recovery. (Of course, the fact
that the user’s files are probably not backed up and that there are copies of
the operating system on the distribution tape have nothing to do with this
decision. The originalversion of Unix sent outside of Bell Labs didn’t come
on distribution tapes: Dennis Ritchie hand-built each one with a note that
said, “Here’s your rk05, Love, Dennis.” (The rk05 was an early removable