linux-kernel - Re: New filesystem for Linux

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Date:	Fri, 3 Nov 2006 00:19:13 +0100 (CET)
From:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
To:	Grzegorz Kulewski <kangur@...com.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: New filesystem for Linux

> Hi,
>
> 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."
>
> Well, maybe I am completly wrong but as far as I understand no disk currently 
> will provide such requirement. Disks can have (after halted write):
> - old data,
> - new data,
> - nothing (unreadable sector - result of not full write and disk internal 
> checksum failute for that sector, happens especially often if you have 
> frequent power outages).
>
> And possibly some broken drives may also return you something that they think 
> is good data but really is not (shouldn't happen since both disks and cables 
> should be protected by checksums, but hey... you can never be absolutely sure 
> especially on very big storages).
>
> So... isn't this making your filesystem a little flawed in design?

There was discussion about it here some times ago, and I think the result 
was that the IDE bus is reset prior to capacitors discharge and total loss 
of power and disk has enough time to finish a sector --- but if you have 
crap power supply (doesn't signal power loss), crap motherboard (doesn't 
reset bus) or crap disk (doesn't respond to reset), it can fail.

BTW. reiserfs and xfs depend on this feature too. ext3 is the only one 
that doesn't.

Mikulas
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