A caster wheel structure contains a body and a connecting shaft. In some embodiments, the charging mechanism includes a user-actuated charging push-button, a reverse charging member coupled to a lancet carrier, and a reverse-motion conversion member coupled therebetween. The first slot duration is provided with a power control signal and the second slot duration is provided with no signal at a partial duration thereof. This distributed copy-on-write includes performing, by a first client, copy-on-write of at least one block of data of the file to be copy-on-written, and performing, by a second client, copy-on-write of at least one other block of data of the file, wherein multiple clients perform the copy-on-write of the file.