linux-ext4 - Re: [RFC] Add new extent structure in ext4

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Message-Id: <4C9A2CF5-A980-43A0-9D43-56EA45DA096C@dilger.ca>
Date:	Wed, 25 Jan 2012 16:03:09 -0700
From:	Andreas Dilger <adilger@...ger.ca>
To:	Dave Chinner <david@...morbit.com>
Cc:	Robin Dong <hao.bigrat@...il.com>, Ted Ts'o <tytso@....edu>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [RFC] Add new extent structure in ext4

On 2012-01-25, at 3:48 PM, Dave Chinner wrote:
> On Mon, Jan 23, 2012 at 08:51:53PM +0800, Robin Dong wrote:
>> Hi Ted, Andreas and the list,
>> 
>> After the bigalloc-feature is completed in ext4, we could have much more
>> big size of block-group (also bigger continuous space), but the extent
>> structure of files now limit the extent size below 128MB, which is not
>> optimal.
>> 
>> We could solve the problem by creating a new extent format to support
>> larger extent size, which looks like this:
>> 
>> struct ext4_extent2 {
>> 	__le64	ee_block;	/* first logical block extent covers */
>> 	__le64	ee_start;	        /* starting physical block */
>> 	__le32	ee_len;		/* number of blocks covered by extent */
>> 	__le32	ee_flags;	/* flags and future extension */
>> };
>> 
>> struct ext4_extent2_idx {
>> 	__le64	ei_block;	        /* index covers logical blocks from 'block' */
>> 	__le64	ei_leaf;	        /* pointer to the physical block of the next level */
>> 	__le32	ei_flags;	        /* flags and future extension */
>> 	__le32	ei_unused;	/* padding */
>> };
>> 
>> I think we could keep the structure of ext4_extent_header and add new
>> imcompat flag EXT4_FEATURE_INCOMPAT_EXTENTS2.
>> 
>> The new extent format could support 16TB continuous space and larger volumes.
>> 
>> What's your opinion?
> 
> Just use XFS.

Thanks for your troll.

If you have something actually useful to contribute, please feel free to post.
Otherwise, this is a list for ext4 development.

I don't encourage XFS users to switch to ext4 (or ZFS, for that matter, since
ZFS can do a lot of things that just aren't possible for XFS, and is now
available for Linux) on your mailing lists, and I'd appreciate the same
courtesy here...

Cheers, Andreas

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