In a classic PATA setup with both storage devices on the same cable, the performance is actually marginally worse than the third case.The fourth case is where things get really interesting, because it’s performance depends almost entirely on the specifics of the hardware setup of the physical storage devices. Some storage protocols may support ‘device-side copy’ functionality (some SCSI devices support this for example, as do most intelligent networked filesystem protocols), in which case this can potentially be rather fast, though usually still slower than the first case. The third case will usually be the slowest case, because the system has to read the data from the device, store it temporarily in RAM, and then write it back out to the device somewhere else. If it does not, then it will generally be equivalent to the third case instead. If it supports reflinks (like ZFS and BTRFS do), then it can be just as fast as the first case (because it essentially becomes the first case). The speed of the second case depends on the filesystem involved. The only two exceptions you would likely ever encounter are dealing with in-line data transformations (such as the in-line compression supported by NTfS) where the source and destination have different rules for such transformations, and dealing with certain networked filesystems (such as older versions of NFS), with both cases becoming equivalent to the third case. In general, the first case is always going to be the fastest, because short of some atypical situations, it just amounts to updating some of the filesystem metadata. Moving or copying a file between two filesystems that are on separate physical storage devices.Moving or copying a file between two filesystems that are on the same physical storage device.Copying a file within a single filesystem.Moving a file within a single filesystem (IOW, within a single ‘drive’ by the Windows definition of the term ‘drive’).In general, there are four cases to consider: It depends on a bit more than just the physical hardware layout.
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