Based on the sessions and from talking with people, nothing beats the NetWare kernel as a file server. Novell said in one of the breakout sessions that the NSS file system on Linux performs 21 to 47 percent slower than it does on NetWare, depending on the workload. NSS on Linux is comparable to some of the other file systems available for Linux.
In a session on optimizing performance on SLES Linux, Novell offered the good advice of using the appropriate file system for the task. If you don't need the rich features of an NSS file system, don't use it. If you have a system that uses lots of temporary files and does its own transaction management, a file system that doesn't have journaling--like EXT2--would be a good choice. If you need to store millions of small files, Riser will be a good choice; because its metadata overhead is less, it will need less space on the disk per file.
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Another issue with NSS on Linux (in my opinion) is that it is limited to the kernel memory space for its file cache buffers. So if you have a box doing nothing but file serving and you have, say, four gigabytes of RAM in it, NSS cache is limited to one gigabyte. And in reality, it's less than that. The NSS team is working to get around that problem, but it sounds like NSS feature trade-offs will be necessary to make it happen.