You try to copy a large file (.iso, .vhd etc) to an external drive which is USB 3.0 compatible.
First, Windows Explorer shows a great transfer rate like 400 MB/s or higher, but in the end the window freezes until you wait a very long time or disconnect your USB drive.
Eventlog does not show any useful information for this issue.
The shown transfer rate can be confusing. Many Dell servers seem to have USB 3.0 not enabled by default!
To be sure it is enabled, open your Dell OMSA web interface -> BIOS Setup or reboot your server into BIOS, then select „Integrated devices“. There should be a USB 3.0 active/inactive option.
Activate it and reboot your server. You might have to install 3rd party USB 3.0 drivers if you use e.g. Windows 2008 R2 or 2012 R2.
Note, if this also does not really help
When copying large files, Windows Explorer status dialog might show incredibly wrong rates in general. To get more realistic values, open Windows Resource Monitor and have a look at your file which is written at that moment („write“ column). You might see your USB 3.0 device writing at about 100 MB/s even if the Explorer dialog shows over 500 MB/s. Even if the dialog status bar is at „100% – finished“, in Resource Monitor you see it keeps writing until it’s really finished, so this could also explain why it seems to hang in the end.