I wan't to install Longhorn on my K8S Cluster, I added two more Harddrives for Storage, is it enough to add them to Server so that they are available as

/dev/sdX

there is no Partition Layout or Filesystem on them.

No, they need to be formatted with a file system

Longhorn support multi-disk but need format the device as supported file systems, e.g.,

xfs

and

ext4

https://longhorn.io/docs/1.4.2/volumes-and-nodes/multidisk/#add-a-disk https://longhorn.io/docs/1.4.2/deploy/install/#installation-requirements

Which Filmformat is more performant xfs or ext4?

The Longhorn team doesn't currently make any recommendations for one underlying file system versus another. The performance testing undertaken in this issue (https://github.com/longhorn/longhorn/issues/2986#issuecomment-923404663) doesn't seem to indicate significant performance differences (compare

Longhorn volume with 3 replicas (host filesystem is ext4)

with

Longhorn volume with 3 replicas; xfs host filesystem

).