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Subject: Re: [PATCH] md/raid0: add config parameters to specify zone layout
To:     Jason Baron <jbaron@akamai.com>, songliubraving@fb.com
Cc:     agk@redhat.com, snitzer@redhat.com, linux-raid@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Guoqing Jiang <guoqing.jiang@cloud.ionos.com>,
        NeilBrown <neilb@suse.de>
References: <1585236500-12015-1-git-send-email-jbaron@akamai.com>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <d8433599-cd4f-80a1-d9f7-8ddad1693850@infradead.org>
Date:   Thu, 26 Mar 2020 08:39:04 -0700
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On 3/26/20 8:28 AM, Jason Baron wrote:
> Let's add some CONFIG_* options to directly configure the raid0 layout
> if you know in advance how your raid0 array was created. This can be
> simpler than having to manage module or kernel command-line parameters.
> 
> If the raid0 array was created by a pre-3.14 kernel, use
> RAID0_ORIG_LAYOUT. If the raid0 array was created by a 3.14 or newer
> kernel then select RAID0_ALT_MULTIZONE_LAYOUT. Otherwise, the default
> setting is RAID0_LAYOUT_NONE, in which case the current behavior of
> needing to specify a module parameter raid0.default_layout=1|2 is
> preserved.
> 
> Cc: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
> Cc: NeilBrown <neilb@suse.de>
> Cc: Song Liu <songliubraving@fb.com>
> Signed-off-by: Jason Baron <jbaron@akamai.com>
> ---
>  drivers/md/Kconfig | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  drivers/md/raid0.c |  7 +++++++
>  2 files changed, 62 insertions(+)
> 
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index d6d5ab2..c0c6d82 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -79,6 +79,61 @@ config MD_RAID0
>  
>  	  If unsure, say Y.
>  
> +choice
> +	prompt "RAID0 Layout"
> +	default RAID0_LAYOUT_NONE
> +	depends on MD_RAID0
> +	help
> +	  A change was made in Linux 3.14 that unintentinally changed the

	                                       unintentionally

> +	  the layout for RAID0. This can result in data corruption if a pre-3.14
> +	  and a 3.14 or later kernel both wrote to the array. However, if the
> +	  devices in the array are all of the same size then the layout would
> +	  have been unaffected by this change, and there is no risk of data
> +	  corruption from this issue.
> +
> +	  Unfortunately, the layout can not be determined by the kernel. If the
> +	  array has only been written to by a 3.14 or later kernel its safe to

	                                                           it's

> +	  set RAID0_ALT_MULTIZONE_LAYOUT. If its only been written to by a

	                                     it has

> +	  pre-3.14 kernel its safe to select RAID0_ORIG_LAYOUT. If its been

	                  it's                                  If it has been

> +	  written by both then select RAID0_LAYOUT_NONE, which will not
> +	  configure the array. The array can then be examined for corruption.
> +
> +	  For new arrays you may choose either layout version. Neither version
> +	  is inherently better than the other.
> +
> +	  Alternatively, these parameters can also be specified via the module
> +	  parameter raid0.default_layout=<N>. N=2 selects the 'new' or multizone
> +	  layout, while N=1 selects the 'old' layout or original layout. If
> +	  unset the array will not be configured.
> +
> +	  The layout can also be written directly to the raid0 array via the
> +	  mdadm command, which can be auto-detected by the kernel. See:
> +	  <https://www.kernel.org/doc/html/latest/admin-guide/md.html#multi-zone-raid0-layout-migration>
> +
> +config RAID0_ORIG_LAYOUT
> +	bool "raid0 layout for arrays only written to by a pre-3.14 kernel"
> +	help
> +	  If the raid0 array was only created and written to by a pre-3.14 kernel.
> +
> +config RAID0_ALT_MULTIZONE_LAYOUT
> +	bool "raid0 layout for arrays only written to be a 3.14 or newer kernel"

	                                              by

> +	help
> +	  If the raid0 array was only created and written to by a 3.14 or later
> +	  kernel.
> +
> +config RAID0_LAYOUT_NONE
> +	bool "raid0 layout must be specified via a module parameter"
> +	help
> +	  If a raid0 array was written to by both a pre-3.14 and a 3.14 or
> +	  later kernel, you may have data corruption. This option will not
> +	  auto configure the array and thus you can examine the array offline
> +	  to determine the best way to proceed. With RAID0_LAYOUT_NONE
> +	  set, the choice for raid0 layout can be set via a module parameter
> +	  raid0.default_layout=<N>. Or the layout can be written directly
> +	  to the raid0 array via the mdadm command.
> +
> +endchoice
> +
>  config MD_RAID1
>  	tristate "RAID-1 (mirroring) mode"
>  	depends on BLK_DEV_MD
> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> index 322386f..576eaa6 100644
> --- a/drivers/md/raid0.c
> +++ b/drivers/md/raid0.c
> @@ -19,7 +19,14 @@
>  #include "raid0.h"
>  #include "raid5.h"
>  
> +#if defined(CONFIG_RAID0_ORIG_LAYOUT)
> +static int default_layout = RAID0_ORIG_LAYOUT;
> +#elif defined(CONFIG_RAID0_ALT_MULTIZONE_LAYOUT)
> +static int default_layout = RAID0_ALT_MULTIZONE_LAYOUT;
> +#else
>  static int default_layout = 0;
> +#endif
> +
>  module_param(default_layout, int, 0644);
>  
>  #define UNSUPPORTED_MDDEV_FLAGS		\
> 


-- 
~Randy
Reported-by: Randy Dunlap <rdunlap@infradead.org>