HyperBac backups twice as slow
We have a 400GB database and have recently purchased HyperBac. Our data and backup volumes are all on an EMC SAN, and prior to installing HyperBac our backups took around 75 minutes. I expected, given the size of the backup files, that I/O would be the main bottleneck and we'd be able to get backup times down to about 15 minutes for an 80GB backup file.
The backup files are certainly 80GB, but they take 2-and-a-half hours to run! Looking at the disk stats, this is what we see:
HyperBac disabled: Backup size 400GB, time taken 75 minutes, Read speed 100MBps, Write speed 100 MBps
HyperBac enabled: Backup size 80GB, time taken 150 minutes, Read speed 50 MBps, Write speed 8 Mbps.
The SAN is clearly capable of reading data at at least 100MBps, so I'd expect at worst that performance would remain the same. Servers are new and have plenty of RAM and cores, SAN storage processors are not overloaded when backups run (it's an office system that has a generous backup window).
So, what's going on?