linux-kernel - Re: [PATCH 0/4] loop: enable different physical blocksizes

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Message-ID: <20150807073330.GB17618@lst.de>
Date:	Fri, 7 Aug 2015 09:33:30 +0200
From:	Christoph Hellwig <hch@....de>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Hannes Reinecke <hare@...e.de>, Jens Axboe <axboe@...com>,
	Alexander Graf <agraf@...e.com>,
	Christoph Hellwig <hch@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] loop: enable different physical blocksizes

On Mon, Jul 27, 2015 at 06:40:57AM -0400, Ming Lei wrote:
> On Fri, Jul 17, 2015 at 3:27 AM, Hannes Reinecke <hare@...e.de> wrote:
> > Currently the loop driver just simulates 512-byte blocks. When
> > creating images for virtual machines it might be required to use
> > a different physical blocksize (eg 4k for S/390 DASD).
> 
> Looks 'qemu-img create' doesn't have parameter of block size,
> so could you share your use case? And I am just curious why
> 512-byte can't work for this case.

The use case is to suppot 4k sectors sizes such as DASDs usually provide,
or just to create a 4k block device to check your filesystem of choice
handles 4k sectors just fine.  Replace 4k with other sector sizes of
your choice for added benefit.  In addition to the DASD use case it's really a
very useful debugging tool.
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