UrBackup Server runs on Linux, Windows and FreeBSD.
There are some issues however if you want advanced features like compression or block level deduplication.
If you want the backups to be compressed the underlying file system has to do that for UrBackup. In most cases this means the operating system has to support that. Since Windows Server 2003/XP Windows has, with NTFS, compression capability.
In Linux following filesystems support compression: ReiserFS: This is not in the standard kernel and probably never will be. You have to compile it. Fuse plugin: Like fusecompress or zfs-fuse/ZFSOnLinux/FreeBSD. Where fusecompress just compresses the files and leaves handling the rest of the file handling to a standard file system. ZFS is a very advanced file system with many features. One of them is compression. It is also able to do block level deduplication and file system level raid.
The backup filesystem has to be able to handle hard links and symbolic links. NTFS is able to handle both (Symbolic links (junctions) are supported since Windows Vista). All Linux/Unix filesystems support hardlinks and symbolic links. FAT does not support this.
The client images are saved into one big file. The filesystem has to be able to handle them. On Windows NTFS supports very big files. You will not have any problems there. On Linux you have to enable the large file support in the kernel and for the specific filesystem. Nowadays this is enabled per default. Then the maximum file size depends on the used file system. With ext3 it can be as small as 16GB if the drive is formatted with a small block size. Usually it is 2TB though (with standard block size).
With deduplication data blocks which are the same in different files are saved only once on the hard disk. ZFS is able to do that. There are also professional storage systems which do deduplication - sometimes in hardware. Btrfs does support out-of-line deduplication. There are some other fuse filesystems which support deduplication but those do not seem to be stable. If ZFS is chosen you should put enough RAM into the backup server otherwise deduplication will cause a huge slowdown. ZFS also allows you to use a SSD as cache device if there is not enough RAM available. UrBackup is build to accomodate a slow deduplicated backup storage. The temporary directory never should be compressed or deduplicated!
UrBackup can also use btrfs in a way that makes deduplication sometimes unncessary. See here.
The client is made for Windows, but the file backup part is also running on Linux.
Limitations in Windows XP/Windows Server 2003:
A image backup cannot be continued. This means if you restart the clients in the middle of a image backup, the backup process has to start anew from the beginning.
Windows XP is the minimal required Windows version.
Image Backups can only be done on partitions which are formatted with NTFS.