linux-ext4 - RE: Extent Depth Histogram Fsck

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Message-ID: <0408C81F72528E40A0D3235A1F67FFC804A3B3@SN2PRD0202MB144.namprd02.prod.outlook.com>
Date:	Tue, 26 Jun 2012 18:07:10 +0000
From:	"Nelson, John R" <John_Nelson@...dent.uml.edu>
To:	Andreas Dilger <adilger@...ger.ca>
CC:	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: RE: Extent Depth Histogram Fsck

ok i see!
So when there are like
3/3/4 that means double index blocks?? How many extents can a single extent index hold in a block?
________________________________________
From: Andreas Dilger [adilger@...ger.ca]
Sent: Tuesday, June 26, 2012 11:40 AM
To: Nelson, John R
Cc: linux-ext4@...r.kernel.org
Subject: Re: Extent Depth Histogram Fsck

On 2012-06-26, at 8:34 AM, Nelson, John R wrote:
> What does the extent depth histogram mean? Is it a measure of something?
>
> like mine is
>
>
> Extent depth histogram: 36010/81

This means that of all the extent-mapped files in the filesystem,
36010 files have an extent tree of depth 0 (i.e. they fit inside the inode)
81 files have an extent tree of depth 1 (i.e. there is a single index block)

Typically, files larger than 4 * 128MB = 512MB need an index block, but if
the maximum-sized extents cannot be allocated then an index block will be needed for smaller files.  Only if you have very large files (> 40GB),
or a very fragmented free space would you need more than a single level
of index blocks.

Cheers, Andreas

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