linux-kernel - Re: New filesystem for Linux

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Date:	Sat, 4 Nov 2006 22:01:11 +0100
From:	Jan-Benedict Glaw <jbglaw@...-owl.de>
To:	Albert Cahalan <acahalan@...il.com>
Cc:	kangur@...com.net, mikulas@...ax.karlin.mff.cuni.cz,
	linux-kernel@...r.kernel.org
Subject: Re: New filesystem for Linux

On Sat, 2006-11-04 14:59:53 -0500, Albert Cahalan <acahalan@...il.com> wrote:
> Grzegorz Kulewski writes:
> > On Thu, 2 Nov 2006, Mikulas Patocka wrote:
> > > As my PhD thesis, I am designing and writing a filesystem,
> > > and it's now in a state that it can be released. You can
> > > download it from http://artax.karlin.mff.cuni.cz/~mikulas/spadfs/
> >
> > "Disk that can atomically write one sector (512 bytes) so that
> > the sector contains either old or new content in case of crash."
> 
> New drives will soon use 4096-byte sectors. This is a better
> match for the normal (non-VAX!) page size and reduces overhead.

Well... VAXen use physical PTEs for 512 byte pages, Linux uses 8
consecutive pages to simulate 4K pages.

On top of that, some of today's machines have configurable page sizes.
Besides that, 512 byte sectors are quite a clever thing: Drives
probably can write a number of consecutive sectors, so if you want to
send a page, just send eight sectors.

> BTW, a person with disk recovery experience told me that drives
> will sometimes reorder the sectors. Sector 42 becomes sector 7732,
> sector 880880 becomes sector 12345, etc. The very best filesystems
> can handle with without data loss. (for example, ZFS) Merely great
> filesystems will at least recognize that the data has been trashed.

Uh? This should be transparent to the host computer, so logical sector
numbers won't change.

MfG, JBG

-- 
      Jan-Benedict Glaw      jbglaw@...-owl.de              +49-172-7608481
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