linux-kernel - Re: New filesystem for Linux

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Message-ID: <Pine.LNX.4.64.0611031252430.17174@artax.karlin.mff.cuni.cz>
Date:	Fri, 3 Nov 2006 12:56:36 +0100 (CET)
From:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
To:	Jörn Engel <joern@...nheim.fh-wedel.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: New filesystem for Linux

>>>> new method to keep data consistent in case of crashes (instead of
>>>> journaling),
>>>
>>> Your 32-bit transaction counter will overflow in the real world.  It
>>> will take a setup with millions of transactions per second and even
>>> then not trigger for a few years, but when it hits your filesystem,
>>> the administrator of such a beast won't be happy at all. :)
>>
>> If it overflows, it increases crash count instead. So really you have 2^47
>> transactions or 65536 crashes and 2^31 transactions between each crash.
>
> I am fully aware the counters are effectively 48-bit.  If they were
> just 32-bit, you would likely have hit the problem yourself already.
>
> Jörn

Given the seek time 0.01s, 31-bit value would last for minimum time of 248 
days when doing only syncs and nothing else. 47-bit value will last for 
reasonably long.

Mikulas