The realtime subvolume is indeed there on Linux, you can make them, mount
them, if you know the correct ioctl call you can make an inode realtime,
it is XFS_IOC_FSSETXATTR, and you need to pass in a struct fsxattr
with fsx_xflags set to XFS_XFLAG_REALTIME and fsx_extsize set to some
value (the unit of allocation for realtime space).
HOWEVER, if you do I/O to this inode then you will hit the wrong partition
on the disk and corrupt your filesystem. I have some code which I think will
fix this, but I have not had a chance to test it yet - it does not break the
rest of xfs though. Even with this code you will have to use direct I/O.
I can package up the code if someone wants to play with it - it should not
corrupt other filesystems, but it could well crash your box. I am not ready
to check it into the tree yet.
And yes, GRIO is a lot more work, and I would debate it being worth the effort
except as an academic exercise for people who like coding.
> Has anyone tried to use linux xfs's realtime section support? although
> publicised, it is there, just manually add 'CONFIG_XFS_RT' to .config in the
> root of your kernel sources. I did finally get this to work, on an lvm,
> mounting /dev/vol/xfs with the option of rtdev=/dev/vol/xfsrt, and at mkfs
> creation time I did not specify extent size. The realtime device is the same
> size as the main volume, although I do not think this is necessary per se, th
> are small, 100M in size, just to test. So far I am looking for as much
> information I can find about realtime volumes, before building a system that
> would heavily use them. Would there be any issues with dumping this filesyst
> I am not sure, but I believe some attribute needs to be set on files to use t
> realtime section, as far as speed is concerned. I am still confused a bit on
> this though, so if someone knows, please let me know. Compiling the kernel w
> this option went without event, some normal warnings is all. This seems stab
> although I do not see why it is not enabled even experimentally in the regula
> configuration tools. Getting GRIO to work with linux would take more doing I
> suppose, and is maybe a 2.5.x kernel subject. On an IRIx 6.5 machine, I saw
> /dev/root mounted with the option 'raw=/dev/rroot'. Is this the realtime sect
> of a IRIX system,.. what looks like a raw device?
> Any input or help in this arena would be appreciated, I have found precious
> little information on it.
> Alan Willis