linux-kernel - Re: Ext3 vs NTFS performance

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Message-Id: <E1Hl1HU-0000h1-8I@be1.lrz>
Date:	Mon, 07 May 2007 13:21:28 +0200
From:	Bodo Eggert <7eggert@....de>
To:	Jörn Engel <joern@...ybastard.org>,
	Christoph Hellwig <hch@...radead.org>,
	Anton Altaparmakov <aia21@....ac.uk>,
	Bernd Eckenfels <ecki@...a.inka.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Ext3 vs NTFS performance

Jörn Engel <joern@...ybastard.org> wrote:
> On Fri, 4 May 2007 10:46:10 +0100, Christoph Hellwig wrote:

>> Which means the right place to fix this is samba.  Samba just need
>> to intersept lseek and pread/pwrite to never allocate sparse files
>> but do the right thing instead.  Now what the right thing would probably
>> be a preallocate instead of writing zeroes, and we need to provide the
>> infrastructure for them to do it, which is in progress currently.
> 
> Why do preallocate and not just truncate the file?

If it's done by samba, it's racy. Only the kernel can reliably tell a
write-beyond-eof from a write-before-eof. Either it should unconditionally
turn these preallocation-writes into truncates, or have a flag which will
turn this feature on and which can be used to turn the lseek into a real
preallocation call.

I don't think unconditionally turning these writes into truncate would be
good, it would change the behaviour of dd bs=1 count=$(($n*$BLOCKSIZE+1)).
-- 
Top 100 things you don't want the sysadmin to say:
17. dd if=/dev/null of=/vmunix

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