Too much time wasted installing fedora on raid1

David Woodhouse dwmw2 at infradead.org
Tue Dec 20 13:20:20 UTC 2005


On Tue, 2005-12-20 at 14:06 +0100, Nicolas Mailhot wrote:
> I don't know how anaconda handles it but the default raid IO limits are
> very conservative (optimized for background work on a live system)
> 
> On a system being created it's probably a better idea to tell the raid
> system to pump as much blocks as possible, since this is a blocking op in
> this context and we don't care about anything else.

I think you miss the point. On a file system which is being created, the
bandwidth limits _ought_ to be fairly much irrelevant. The file system
is _empty_, and the total amount of I/O to create an empty RAID-1 ought
to be almost exactly the same amount of I/O which it takes just to run
'mkfs' twice. The blocks which aren't yet used by the filesystem don't
matter; you shouldn't need to sync their contents.

RAID is just a hack which hides the redundancy from the file system; the
kind of thing we always used to have to do for DOS compatibility so that
we could provide an INT 13h handler and have it 'just work'. It's much
the same reasoning which led to the built-in 'translation layers' on
cheap CF cards and USB sticks which so often eat your data and which
have a tendency to use up their limited lifetime in copying obsolete
sectors belonging to deleted files around on the underlying medium.

We don't _need_ that kind of layering in Linux. Have a library of
functions which can be used for such redundancy, by all means -- but
don't just make RAID pretend to be a 'standard' block device and prevent
all possibility of sharing knowledge between the file system and the
layer providing the redundancy. That's just insane.

-- 
dwmw2




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