linux-ext4 - Re: Maximum number of directories

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Message-ID: <alpine.LFD.2.00.1302051538270.3225@localhost>
Date:	Tue, 5 Feb 2013 15:43:51 +0100 (CET)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	Tvrtko Ursulin <tvrtko.ursulin@...lan.co.uk>
cc:	Lukáš Czerner <lczerner@...hat.com>,
	Prashant Shah <pshah.mumbai@...il.com>,
	linux-ext4@...r.kernel.org
Subject: Re: Maximum number of directories

On Tue, 5 Feb 2013, Tvrtko Ursulin wrote:

> Date: Tue, 05 Feb 2013 14:30:24 +0000
> From: Tvrtko Ursulin <tvrtko.ursulin@...lan.co.uk>
> To: Lukáš Czerner <lczerner@...hat.com>
> Cc: Prashant Shah <pshah.mumbai@...il.com>, linux-ext4@...r.kernel.org
> Subject: Re: Maximum number of directories
> 
> 
> Hi,
> 
> On Tuesday 05 February 2013 14:06:14 Lukáš Czerner wrote:
> > On Mon, 4 Feb 2013, Tvrtko Ursulin wrote:
> > > Date: Mon, 04 Feb 2013 13:36:29 +0000
> > > From: Tvrtko Ursulin <tvrtko.ursulin@...lan.co.uk>
> > > To: Prashant Shah <pshah.mumbai@...il.com>
> > > Cc: linux-ext4@...r.kernel.org
> > > Subject: Re: Maximum number of directories
> > > 
> > > On Monday 04 February 2013 18:49:54 Prashant Shah wrote:
> > > > Hi,
> > > > 
> > > > On Mon, Feb 4, 2013 at 4:25 PM, Tvrtko Ursulin
> > > > 
> > > > <tvrtko.ursulin@...lan.co.uk> wrote:
> > > > > I was creating such a (crazy?) tree and hit -ENOSPC at ~31 million
> > > > > directories created in total with df showing only 40% use:
> > > > > 
> > > > > Inode count:              29868032
> > > > > Free inodes:              29848131
> > > > 
> > > > Since, each directory will use a inode entry, there is some mismatch
> > > > with ~31 million directories and 19901 inodes in use. The inode usage
> > > > count should be much larger. You have max 29 million inodes available
> > > > - so max can be 29 million directories.
> > > 
> > > Yeah, I totally forgot about the inode situation on ext filesystems. So is
> > > tune2fs giving wrong stats for live (mounted) filesystems?
> > 
> > Not sure what situation you're referring to. Directory as any other
> > file is represented by an inode and there is a limited number of
> > inodes in the file system.
> 
> The situation that inode blocks are statically allocated at mkfs time.

Yes, that is true.

> 
> > Using tune2fs on live/mounted file system is bad idea and the
> > information might not be correct (exactly for this reason it is
> > _NOT_ recommended to run fsck on live file system). Use 'df -i' if
> > you want to get information about inode count.
> 
> Yes, later I figured out that tune2fs -l does not give current stats for live 
> filesystems. I did not expect that to be dangerous though. And I also forgot 
> about 'df -i'. Thing is, I did not hit this limit since the previous century 
> so guess I subconsciously assumed inode limits are an outdated concept. :) 

Running tune2fs -l on live file system is not dangerous, I did not
said that. Running fsck on live file system on the other hand _is_
dangerous.

-Lukas

>  
> Regards,
> 
> Tvrtko
> 
>