Why the volume size on tape is different to the volume size of data ingested?
After a workflow execution, you can see a difference between the volume size of what is stored on tape and the capacity processed by the workflow.
The reason is that the Tape Drive has compression capabilities ; and this hardware compression process can be significant. The hardware compression is much faster than software compression, it is transparent to the operating system, and data is compressed “on the fly”.
Usually, the compression ratio for magnetic tape drives is maximum 2:1. In fact, the compression ratio of 2:1 may be really equal to 1.2:1 or 1.6:1. That depends on the type of data that you are writing onto tape. If the data are already compressed or not.
To know more about the level of compression of your tapes, you can check if the tape drive compression setting is activated. You can also see the compression status of each tape, for that, you can access the Nodeum Tape reporting to see the level of compression of each media:
If you want to verify if each file has been well copied to tape; we recommend to activate the Checksum Integrity verification during the workflow execution.
Nodeum supports the two main algorithms: md5-hash and xxhash-64be.
And then you have also the option to compare each checksum and then validate if all files have been well copied on the tape.