Rich K.
all running perfectly fine
If the totality of your data is only on those 4 drives,... take caution and consider at least one mirror of that data is unconnected until resolution.
Reports range from immediate to 3+ days before data corruption occurs (possible point at which a time machine backup occurs).
Though some reports come across that bare formatted drives via USB are affected, it is unknown if these persons in fact have, unwittingly, lingering WD software installed.
Ignoring the sleep 'issue' between Firewire and thunderbolt which is of very minor importance and a seperate occurrence,.....there is all indication increasingly so, that while most (or quickest affected) affected in these threads are WD MyBook.
There is more than sufficient indication that non-RAID bare USB formatted simplex enclosure HD are being affected. (but as to lingering WD software installed...?)
Ignoring the 5% of reports, for purpose of clarity of 'most' occurances,... indications all point to: 1. RAID, 2. WD software, ...& Mavericks incompatibility between both or either of these two.
Peace 😊