Which gigabit netgear switch is best for jumboframes ?

NilsG wrote:
TX and RX errors is alway zero

That would tend to rule out any cabling.

NilsG wrote:
Just now I am replacing disks in this ultra6 nas (some 24 hours restriping left on the third 3TB disk @35% - and three more to come)... ~850 Mbps down and some ~520Mbps up - yeah I know it's not "slow" but as said before a huge difference between up/down

Are you testing during the resync? That definitely will slow the NAS down

NilsG wrote:
...the hacky upload explains itself with the workload between the smb process and the raid parity process. The nas can't balance the 2 process perfectly, so it first cache the data to write, then slow the upload to process the parity.

I'm not sure I would say it exactly that way, but there is at least one disk read and two disk writes that need to happen for every write to the raid array. However, unlike read requests, this I/O can be can be queued.

You should make sure that the disk write cache is enabled, and the "disable full system journaling" option is also checked on the system/performance tab in frontview. BTW, if you don't have a UPS protecting the NAS you should get one - especially if you are using these settings.

NilsG wrote:
As said I have three GS108s - what is meant with co-located ?

Co-located means in the same location. Yours are not, so consolidating them into one bigger switch isn't possible (unless you rewire the house).