>
> Can I use and benefit from an rt section without making a specific inod
> e
> realtime? Or does it only benefit inodes that have been made 'realtime'. Do
> es
> it have any specific overall fs performance effect? My test is small, so it
> is
> fast anyway. also, is there any size guideline to the sizes of rt sections vs
> size of the data and log sections? Or does it only matter to the inodes that
> are used in a realtime fashion?
>
> Alan Willis
> alan@xxxxxxxxx
>
The realtime subvolume is where data for realtime inodes is allocated, so yes
it only applies to those. Create a new file, make it realtime, and then do
I/O to it. Realtime is a little bit of a misnomer, the differences are:
o There is only data in the partition, all metadata remains the the data
subvolume. If you put the partitions in the correct place then the only
time headseeks happen is to go and get actual data, no log or metadata
I/O to get in the way.
o A different space allocator is used, it uses a binary chop type approach
to disk space which is wasteful, but which means it is very hard to
fragment the files on realtime partitions. This allocator is also faster
and tends to allocate space in a more deterministic amount of time.
o When you make the filesystem, and when you create a realtime file via the
ioctl call you can specify an extent size, all allocations will be a
multiple of this. I have my doubts that this will work as advertised yet
on linux.
These are all supposed to add up to something which is good for doing streaming
I/O, typically of very large files such as video data.
Here are the changes I have to at least attempt to send disk I/O to the
realtime device.
Users of realtime on Irix would probably create a filesystem which was almost
all realtime space, you still need the regular partition for the log and the
metadata.
Steve
realtime.patch
Description: realtime.patch
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