Hi,
On 02/09/2012 01:50 PM, richard -rw- weinberger wrote:
On Thu, Feb 9, 2012 at 1:38 PM, João Pagaime<j...@fccn.pt> wrote:
here's a short summary by FS:
• ----------------(RW)… you are using FUSE.
No, I'm not using FUSE.
My OpenNebula cluster is built on top of ocfs2.
Richard meant that the XtreemFS client implementation does use FUSE just
as many other distributed file systems do.
Regarding the general FUSE performance discussion:
On 02/09/2012 11:49 AM, richard -rw- weinberger wrote:
[...]
> Hmm, you are using FUSE.
> Performance measurements would be really nice to have.
>
Any suggestions how to conduct OpenNebula specific measurements are welcome.
On our mailing list I wrote about the write throughput performance of
XtreemFS: http://groups.google.com/group/xtreemfs/msg/f5a70a1780d9f4f9
Write throughput is usually limited by the execution time of the write
operation since the application on top does not issue the next write()
before the previous did return. Therefore we also allow asynchronous
writes which acknowledge a number of write()s to the application before
they are actually confirmed by the storage server. To be on the safe
side in that case, you have to execute fsync() and evaluate the return
value of close(). As written in the post mentioned above, with
asynchronous writes you are able to almost max out a GbE link (up to
100MB/s write speed), but it also incurs a lot of overhead: I saw up to
70% CPU usage for the XtreemFS client during that test.
> Writing fancy file systems using FUSE is easy. Making them fast and
scalable
> is a damn hard job and often impossible.
I fully agree that kernel-based file systems in Linux will always have a
lower overhead than its FUSE counterparts. But the overhead is mainly
caused by the structure of the Linux kernel: all data read and written
by FUSE file systems has to be copied between kernel space and user
space. If this was optimized, the overhead would be much less significant.
In general, the overhead of a FUSE implementation is the cost of the
"fanciness". If a required feature is only available in a FUSE based
file system, you would rather use that than waiting for a never
appearing kernel implementation. Writing a distributed file system in
the kernel is a damn hard job and often impossible. Therefore FUSE file
systems are an alternative.
The scalability (of a distributed file system) is independent of the
choice of a kernel or userspace implementation. That's a matter of the
design of the file system.
At the end it's up to the user. If there's a kernel based file system
available which suits your needs, than you can use that (as in your
case). If not, you're willing to pay the price for the overhead since
the FUSE based file system has a lot more to offer.
Best regards,
Michael
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