Piergiorgio Sartor <piergiorgio.sartor@xxxxxxxx> writes:
> Hi all,
>
> question for the experts.
>
> It would be possible, excluding performances, to
> build an user-space RAID system?
>
> I mean, something like fuse does, with a user space
> daemon to perform the math, especially for RAID-6,
> and the rest, together with a small kernel module.
>
> Or there are technical limitations which make this
> approach impossible with the current architecture?
>
> Just curious,
>
> bye,
You can use fuse to create a filesystem containing just one file,
which represents your user-raid, and mount that loopback. Since you
can already do it it can't be impossible. It just isn't optimal.
If you are truely interested then look at fuse and cuse and create a
buse along the same lines. I have a few features I would like to see:
1) zero-copy (with splice()?)
Currently fuse calls read() to get the data for a write
request. This copies the data into the supplied buffer.
It would be better if one could splice() the data into a pipe and
then splice it back onto the actual device/file the data resides
on.
2) async crypto api support
Some hardware has support for XOR or AES. The kernel has a nice API
for this supporting both software and hardware drivers. It would be
nice if one could interface with that API from userspace. For good
performance this should be zero-copy again. So one would just
splice the data into it and splice the result out of it.
3) barrier support
Currently (last I checked) the loopback device has no barrier
support and I'm not sure how fuse should act on barriers.
A buse [Block device in User SpacE] (like fuse and cuse) should
have a callback for barriers and probably not use the loopback hack.
4) block ioctl support
Fuse has a callback for ioctls. Not sure if that is sufficient to
handle block ioctls or if something needs to be added there. But it
would be nice if one could request the size and geometry and so on.
MfG
Goswin
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