Objects are assigned to stripes based on a hash. The seed string for this hash is computed from properties of the storage. This means that if the storage is changed in any way, the hashing changes which disrupts assignment on all other stripes.
An actual example is for a deployment that uses /dev/sdb .. /dev/sdx. If one of these disks fails (say /dev/sdm) then all of the other drives will "move down' at the next system restart which will in turn change the hash seed string for them which will make almost all of the cached objects on those drives inaccessible. Losing a single drive could wipe out most of the cache.
This fix allows an administrator to specify the hash seed string in the storage.config file. The seed strings (and hence the resulting hash) can be kept consistent for a physical device even if the operating system assignment is changed.
P.S. As a side note for Linux users, there are symlinks for raw disk devices in /dev/disk. These can be used in storage.config to avoid some of these problems.