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List:       ceph-devel
Subject:    Re: [PATCH v3 0/2] Add ceph root filesystem
From:       Mark Doffman <mark.doffman () codethink ! co ! uk>
Date:       2014-06-05 19:13:31
Message-ID: 5390C15B.4060407 () codethink ! co ! uk
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On 05/28/2014 06:46 PM, Alex Elsayed wrote:
> mark.doffman@codethink.co.uk wrote:
>
>> From: Mark Doffman <mark.doffman@codethink.co.uk>
>>
>> Hi All,
>>
>> The following is a third version of a patch series that adds the ability
>> to use a ceph distributed file system as the root device.
> <snip>
>
> Would you mind expanding on why you want to do this in the kernel, instead
> of using an initramfs? For example, dracut supports the following syntax,
> and sets it up using the same tools as mounting NFS in a running system
> rather than the kernel's nfsroot support:
>
> root=nfs:[<server-ip>:]<root-dir>[:<nfs-options>]
> root=nfs4:[<server-ip>:]<root-dir>[:<nfs-options>]
> root={dhcp|dhcp6}
>
> root=dhcp alone directs initrd to look at the DHCP root-path where NFS
> options can be specified.
>
> It also supports CIFS, as a further illustration:
>
> root=cifs://[<username>[:<password>]@]<server-ip>:<root-dir>
>
> Extending this to Ceph seems much simpler than implementing such a thing in
> the kernel, especially given dracut's modular nature, and it's easy enough
> to compile an initramfs into the kernel.

An initramfs, and dracut, has been mentioned before as a possible 
solution. The reason I would prefer this in the kernel is simplicity. 
NFS root is in the kernel and we regularly use it without an initramfs.

However simple dracut is still a more complex procedure, for something 
that is very easy to do in the kernel.

Using a root device also has the advantage that it might produce smaller 
images for memory constrained devices.

>
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