File transfer speeds can vary greatly depending on many factors. CopyQueue reports progress as accurately as it can, but real-world performance may differ from the initial estimates. Here are the most common reasons a transfer might be slower than expected:
Your transfer speed is always capped by the slowest link in the chain. This may be:
Even if your Mac supports fast speeds, the destination or connection type might not.
There are different methods for estimating the remaining time, so macOS and other software will produce different time estimates to CopyQueue. Sometimes an initial estimate is misleading, but becomes more accurate when more data has been copied. The actual transfer speed itself can also fluctuate for many reasons:
This can cause the “time remaining” value to jump up or down unexpectedly.
When a new file is created, there is more work involved than just transferring the data. The file must be created in the file system, along with any containing directories, specifying metadata values and permissions. If the file size is very small (eg. less than 1KB), this overhead may be more time consuming than actually copying the data. It is also difficult to estimate, because the file creation time is not related to the data transfer rate, and depends on the transfer protocol and destination file system.
So transferring thousands of small files will be much slower than copying a single large file of the same size.
Drives can slow down if they are:
CopyQueue is designed to transfer files one at a time, specifically to avoid the effects of concurrent copying. But any external file operations will still reduce overall transfer speed.
If you’re copying over a network share (SMB, AFP, NFS), speed is affected by:
Network transfers often have more variability than local copies.
There are some other less common factors which could affect transfer speed, such as: