Generally speaking, the hardware compression is performed on the data path level. As a matter of fact, the hardware compression is only available for the data path which directs data to tape libraries. Under this circumstance, the uncompressed data will be sent from the client computer to the media through the data path. Therefore, the data will be compressed by the tape drive hardware before being written to the media.
There is no doubt that hardware compression is faster than software compression most of the time. The reason is that hardware compression is operated by dedicated circuitry. As a result, the hardware compression is ideal for direct-connect configurations in particular where the subclient and MediaAgent are hosted by the same physical computer. In such configurations, the drives are able to compress the data at the same rate as it is sent by the subclient as there are no network bottlenecks throttling the data transmission to the media drives. On the other hand, the hardware compression can boost the virtual capacity of the tape but also the performance of the data protection thanks to the tape storing more data per unit with higher operation speed.
However, the problem is that hardware compression is not supported by disk library. It is only applicable for tape libraries.
If the data secured by data protection operations must compete with other data for network bandwidth, then hardware compression may be not that useful. When the network is congested, the tape drives will be starved for data for the data cannot be supplied quickly enough. Under such circumstance, the drives can compress as well, but the drives are likely to stop and restart the media in order to wait for more available data. Therefore, the compression performance may not be very ideal, which may lead to some potential problems.