I've huge problems with backup of Hyper-V on handful of HOSTS. During backup done by the software some machines become unavailable, host starts dying etc. We tracked this to not the software itself but file copying. Just doing file copy from drive D to C of size 30GB will kill off the HOST during file transfer. The ram usage before file copy is 48gb used out of 64GB. When you start the transfer of 30GB file the usage of ram changes and in 1 minute it's 64 out of 64 server starts crawling and even RDP, physical access stops working until the file copying is done. So during backup it can take hours for the servers to be avaialble.
This is a DELL Server R515 with RAID controller in mode Write-back. I've noticed this on other Windows 2012 servers. I tried using some old solutions to disable cache from 2003 but none are working. I've tested it on both IBM and Dell servers and behaviour was very similar. Ram usage going up. First it's starts with 700MB/s speed copy and then after ram is used it's going slowly. So the question is how to disable file caching or limit it to normal values.
Please don't give suggestions to use robocopy, or other "copying" tools because while it may solve the problem with copying by using external software my problem is actually about backups taken by 3rd party software which i have no influence on. I would like "Explorer" to behave normally :-)
Run this as administrator at the command line:
You can set three values to this entry: 0 for not set, 1 for default, and 2 for increased.
What is killing your server is not disk caching or ram usage per-se, rather the copy operation itself. In fact, non-dirty pages can be immediately reclaimed if memory pressure occurs.
Basically, during the copy you are constantly submitting I/O requests faster than the disks can handle, bringing the system to a crawl. While disabling the write back caching (both at OS and RAID card level) can give somewhat better performance, the real solution is to schedule such operating during a low load time (eg: night hours) or, alternatively, you can throttle back the copy speed (to not burn all available IOPS).
Just so anyone is wondering... it acted like that on Windows Server 2012. Upgrade to Windows Server 2012 R2 helped. Microsoft refused to patch it because they said it's a problem with Dell (they did all the troubleshooting and pointed at cache issues), and Dell refused to help because apparently the server was bought without a license which is only partially true because the server was actually bought with a license from Dell but thru reseller which most likely did sell from 2 different sources.
So we bought a new license and servers worked after that. Still pain.