I have made a backup copy job for our two physical Exchange servers, and for the first time it has made a weekly fullbackup according to our GFS archive policy. It turned out well eventually, but it went on for ages... The creation of the GFS weekly fullbackup took 12 hours and 30 minutes. And then the creation of the new synthetic fullbackup for the backup copy chain took an additional 14 hours and 37 minutes, making a total of just over 27 hours... The fullbackup files are approx. 5.6 TB in size, and that may be considered very large, or it may not, I don't really know... But come on! 27 hours?!
We have three identical state-of-the-art, top-of-the-line, cutting-edge HP DL380 G10 servers, each with two Smart Storage Arrays of 90 TB, using RAID 5, and 384 GB of RAM. The best you can get for money, basically... One of the servers is dedicated for archival purposes, so the backup copies are put there.
If all this agony is caused by the mistake that Microsoft made regarding ReFS performance in a Windows Update in May (which is said to be fixed in July), then this must be the biggest mistake that Microsoft has ever made, throughout the history of time!