linux-ext4 - Re: EXT4 data block allocation alignment

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Date:	Wed, 11 Jun 2014 15:03:59 +0200 (CEST)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	Teng-Feng Yang <shinrairis@...il.com>
cc:	linux-ext4@...r.kernel.org
Subject: Re: EXT4 data block allocation alignment

On Wed, 11 Jun 2014, Teng-Feng Yang wrote:

> Date: Wed, 11 Jun 2014 19:44:49 +0800
> From: Teng-Feng Yang <shinrairis@...il.com>
> To: linux-ext4@...r.kernel.org
> Subject: EXT4 data block allocation alignment
> 
> Hi, folks,
> 
> Recently I have been working on a small project which requires data
> blocks of each file to be aligned to 512KB/1MB boundary for
> performance reason. As far as I know, this can be accomplished by
> setting the stripe unit on XFS or enabling the "bigalloc" feature on
> EXT4. However, the "bigalloc" feature has not yet been stated to be
> stable in the latest release. So, this makes me wondering if I can
> achieve this block allocation alignment by setting the stride-size on
> EXT4. The document of mke2fs only says that this value may be used by
> the block allocator, so I am not quite sure what it can offer for me
> in this case.

Even though bigalloc will work like that it's just nice side effect
of that feature. But, yes it should work.

However please see mke2fs manual page. Ext4 also have options to
make allocations aligned (stride, stripe_width).

There is also "stripe" mount option, but you should not need to set
that it you set it on mkfs time.

Thanks!
-Lukas

> 
> Any help would be appreciated.
> Thanks,
> 
> Dennis
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