The restores can be significantly slower than backups. It is hardly a surprising observation when we realize there are several aspects that could make the former comparatively slower. Multiplexing is a substantial one among the causative factors.
The whole concept of multiplexing is based on broadcasting signals from a variety of sources over an individual transmit medium for maximized usage and storing the data value.
Multiplexing comes with its own set of significant advantages. Yet, if we analyze statistics from the past two decades, we can see that there has been a substantial shift from tape for storage to other sources.
Multiplexing is an influential factor that impacts the speed of restores if you are copying data from tape. However, copying from other sources such as disks is usually free of multiplexing-related impacts on the restore speeds.
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To explain it, consider a scenario; imagine that you have to restore data from a multiplexed source, say tape. A backup software should read the tape and eliminate all the streams except the one in focus. Overall, this could be a time-consuming process and may impact the speed of the restores.
However, it is imperative to mention that multiplexing is not the sole reason impacting the speed of restores. Here is a brief look at the other causes that reduce the rate of restores.
High transactional logs on databases can affect the speed at which the data is restored.
Writing into file systems, if there are several files, say millions of them, can cause the speed to reduce. When restoring files, there has to be a file creation to which the data could be fixed. This fie creation can usually take longer sometimes.