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Date: Mon, 29 Dec 2014 17:55:33 +0800
From: Anand Jain <anand.jain@oracle.com>
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To: Ankur Tank <Ankur.Tank@LntTechservices.com>
CC: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: btrfs doesn't format eMMC if previous filesystem is ext4
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     That's by design. More over this is nothing specific to eMMC.

Thanks.

On 29/12/2014 15:15, Ankur Tank wrote:
> Hi Anand,
>
> Precondition : Previous filesystem on eMMC  was --- ext4----
> Use case : Now format eMMC to btrfs format, using ---mkfs.btrfs---
> mkfs.btrfs denies formatting eMMC telling that eMMC contain an existing filesystem(ext4).
>
> In my opinion mkfs.btrfs must allow to format eMMC with btrfs even if there is other filesystem on it.
>
> mkfs.ext4 and mkfs.f2fs does allow formatting even if eMMC contains some other file system on it.
>
> Note: If I add "-f" option mkfs.btrf does allow formatting eMMC to btrfs filesytem.
>
> Regards,
> Ankur
> -----Original Message-----
> From: Anand Jain [mailto:Anand.Jain@oracle.com]
> Sent: Monday, December 29, 2014 8:21 AM
> To: Ankur Tank; linux-btrfs@vger.kernel.org
> Subject: Re: btrfs doesn't format eMMC if previous filesystem is ext4
>
>
>
> On 12/26/2014 11:24 PM, Ankur Tank wrote:
>> Hi,
>>
>> I wanted to test btrfs on the eMMC of beaglebone black based custom board.
>> Precondition: eMMC is formatted with ext4 filesystem Use case:
>>           Format eMMC with mkfs.btrfs  -L  <label>  <dev>
>> Result:
>>           Mkfs.btrfs denies formatting eMMC because its existing
>> filesystem
>>
>> # mkfs.btrfs -L "1storage" /dev/mmcblk0p2
>> /dev/mmcblk0p2 appears to contain an existing filesystem (ext4).
>> Error: Use the -f option to force overwrite.
>>
>> If I add "-f" its possible to format the eMMC.
>>
>> # mkfs.btrfs -f -L "1storage" /dev/mmcblk0p2 Detected a SSD, turning
>> off metadata duplication.  Mkfs with -m dup if you want to force metadata duplication.
>> Btrfs v3.17
>> See http://btrfs.wiki.kernel.org for more information.
>>
>> Performing full device TRIM (1.72GiB) ...
>> Turning ON incompat feature 'extref': increased hardlink limit per
>> file to 65536 [273917.692896] btrfs: device label 1storage devid 1
>> transid 3 /dev/mmcblk0p2 fs created label 1storage on /dev/mmcblk0p2
>>           nodesize 16384 leafsize 16384 sectorsize 4096 size 1.72GiB
>>
>> I had downloaded debian package from following link
>> https://packages.debian.org/sid/armhf/btrfs-tools/download
>>
>> Is it a bug ? or I am missing something ?
>    I don't see any bug. Can you be more specific ? Thanks.
>
>> Thank you,
>>
>> Regards,
>> Ankur
>> L&T Technology Services Ltd
>>
>> www.LntTechservices.com<http://www.lnttechservices.com/>
>>
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> L&T Technology Services Ltd
>
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>
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