linux-kernel - Re: UBIFS vs Logfs (was [RFC PATCH] UBIFS

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Date:	Tue, 01 Apr 2008 14:17:04 +0300
From:	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
To:	Jörn Engel <joern@...fs.org>
CC:	Artem Bityutskiy <dedekind@...dex.ru>,
	Adrian Hunter <ext-adrian.hunter@...ia.com>,
	Jan Engelhardt <jengelh@...putergmbh.de>,
	LKML <linux-kernel@...r.kernel.org>, joern@...ybastard.org
Subject: Re: UBIFS vs Logfs (was [RFC PATCH] UBIFS - new flash file system)

Jörn Engel wrote:
> Fair enough.
> 
> The obvious downside of all this is depending on UBI, which has a linear
> scan.  My goal was to avoid the linear scan completely.  It is a harder
> goal and I haven't reached it yet.  Imo it is reachable and I will
> continue going in that direction.

Yes, it was our core design decision. One of the reasons, we were not sure
this is technically possible to do on bare flashes. I mean, it just looked
so complex to have all in one, so we figured that was a good split, where
you can cut on big work on two smaller separate ones. The benefit of this
is obvious - we have created a complete system, which is not perfect though
and have scalability issues.

Our point is that UBI is scalable enough for the time being.

I wrote some documentation about this in UBI FAQ and UBIFS FAQ:
http://www.linux-mtd.infradead.org/doc/ubifs.html#L_scalability

We can now improve scalability of UBI without affecting UBIFS - it has some
potential. And we may develop UBI2 which would be more much more scalable,
but this is a big project and we are not planning to do this so far. Others
could do.

So in other words, using UBI allowed us to get a finished system faster. I
meets our's and many other people's requirements, although it has issues if
you try to use it on really huge flashes, like 64GiB. That's a drawback.
But the good thing is that this would require re-working UBI layer, without
complete re-working of UBIFS. 

> You picked the route of using UBI, which makes a lot of stuff easier.
> It is a fair approach and I don't mind you taking it.  It has drawbacks,
> but so has everything else.
Agree.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
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