linux-kernel - Re: VFAT truncate performance

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Date:	Tue, 05 Sep 2006 16:55:14 +0200
From:	Xavier Bestel <xavier.bestel@...e.fr>
To:	Mattias Rönnblom <hofors@...ator.liu.se>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: VFAT truncate performance

On Tue, 2006-09-05 at 15:52, Mattias Rönnblom wrote:
> Hi,
> 
> extending files by ftruncate(2) runs very slow on VFAT file
> systems. On my USB harddisk w/ VFAT, it takes 14 seconds to extend an
> empty file to 1 GB. On a memory stick, it takes well over 4 minutes.
> 
> My question is: is this problem on the conceptual level (ie there is
> no way of extending files on FAT that doesn't involve many disk
> operations) or is the current Linux fs driver suboptimal in this
> respect?
> 
> The reason for asking is that I run Samba which service files on USB
> devices (w/ VFAT for portability) to Windows XP clients. When copying
> files to the Samba server, Microsoft SMB clients seem to extend the
> file before actually starting to copy the data. This results in
> sluggishness and timeouts when copying large files to VFAT
> filesystems.

Is your USB stick mounted -o sync ? If that's the case, the truncate()
and write() won't be merged so they will take twice as long. -o sync
generally kills performance on USB sticks.

	Xav

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