Date: Mon, 18 Aug 2003 10:07:11 +1000
From: Nathan Scott <nathans@sgi.com>
To: girish dudhe <girish_dudhe@yahoo.com>
Cc: linux-xfs@oss.sgi.com
Subject: Re: How large file store in XFS
Message-ID: <20030818000711.GA1251@frodo>
References: <20030816065428.56233.qmail@web40410.mail.yahoo.com>
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On Fri, Aug 15, 2003 at 11:54:28PM -0700, girish dudhe wrote:
> hi all,
> 
>    In XFS,whole file systen is divided into number of
> allocation group. e.g. Consider size of the file
> system is 1GB ,then  it will create eight allocation
> group that means each has 125 MB.Each allocation Group
> has its own inodes and data blocks.

That is correct.

>    Now I want to store the file of size 500MB.How it
> gets stored ? Whether it gets stores in one allocation
> group or multiple allocation group? 

Since it cannot be stored in one allocation group (500 > 125),
it will be stored in multiple AGs (assuming it is not a sparse
file ;).  File extent maps use the full disk addresses, and so
are not allocation group relative and can span multiple AGs if
necessary.  A single extent can never span more than one AG.

The xfs_bmap(8) command will show you the block map for a
given file, and you can see which allocation group each of
the extents lives in using the -v option, iirc.

cheers.

-- 
Nathan