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Re: [dm-devel] [PATCH] DM RAID: Add support for MD RAID10 personality



On Tue, 26 Jun 2012 07:03:51 -0500 Jonathan Brassow <jbrassow redhat com>
wrote:

> dm raid: add md raid10 support
> 
> Support the MD RAID10 personality through dm-raid.c
> 
> Signed-off-by: Jonathan Brassow <jbrassow redhat com>
> 
> Index: linux-upstream/drivers/md/dm-raid.c
> ===================================================================
> --- linux-upstream.orig/drivers/md/dm-raid.c
> +++ linux-upstream/drivers/md/dm-raid.c
> @@ -11,6 +11,7 @@
>  #include "md.h"
>  #include "raid1.h"
>  #include "raid5.h"
> +#include "raid10.h"
>  #include "bitmap.h"
>  
>  #include <linux/device-mapper.h>
> @@ -52,7 +53,11 @@ struct raid_dev {
>  #define DMPF_MAX_RECOVERY_RATE 0x20
>  #define DMPF_MAX_WRITE_BEHIND  0x40
>  #define DMPF_STRIPE_CACHE      0x80
> -#define DMPF_REGION_SIZE       0X100
> +#define DMPF_REGION_SIZE       0x100
> +#define DMPF_RAID10_NEAR_COPIES 0x200
> +#define DMPF_RAID10_FAR_COPIES  0x400
> +#define DMPF_RAID10_FAR_OFFSET  0x800
> +
>  struct raid_set {
>  	struct dm_target *ti;
>  
> @@ -66,6 +71,15 @@ struct raid_set {
>  	struct raid_dev dev[0];
>  };
>  
> +/* near_copies in first byte */
> +/* far_copies in second byte */
> +/* far_offset in 17th bit */
> +#define ALGORITHM_RAID10(near_copies, far_copies, far_offset) \
> +	((near_copies & 0xFF) | ((far_copies & 0xFF) << 8) | ((!!far_offset) << 16))
> +#define RAID10_NC(layout) (layout & 0xFF)
> +#define RAID10_FC(layout) ((layout >> 8) & 0xFF)
> +#define RAID10_FO(layout) (layout & 0x10000)
> +
>  /* Supported raid types and properties. */
>  static struct raid_type {
>  	const char *name;		/* RAID algorithm. */
> @@ -76,6 +90,8 @@ static struct raid_type {
>  	const unsigned algorithm;	/* RAID algorithm. */
>  } raid_types[] = {
>  	{"raid1",    "RAID1 (mirroring)",               0, 2, 1, 0 /* NONE */},
> +	{"raid10",   "RAID10 (striped mirrors)",        0, 2, 10, -1 /* Varies */},
> +	{"raid1e",   "RAID1E (Enhanced RAID1)",         0, 2, 10, -1 /* Varies */},
>  	{"raid4",    "RAID4 (dedicated parity disk)",	1, 2, 5, ALGORITHM_PARITY_0},
>  	{"raid5_la", "RAID5 (left asymmetric)",		1, 2, 5, ALGORITHM_LEFT_ASYMMETRIC},
>  	{"raid5_ra", "RAID5 (right asymmetric)",	1, 2, 5, ALGORITHM_RIGHT_ASYMMETRIC},
> @@ -339,10 +355,17 @@ static int validate_region_size(struct r
>   *    [max_write_behind <sectors>]	See '-write-behind=' (man mdadm)
>   *    [stripe_cache <sectors>]		Stripe cache size for higher RAIDs
>   *    [region_size <sectors>]           Defines granularity of bitmap
> + *
> + * RAID10-only options:
> + *    [raid10_near_copies   <# copies>] Near copies. (Default: 2)
> + *    [raid10_far_copies    <# copies>] Far copies.  (Default: 1)
> + *    [raid10_far_offset    <0/1>]      Offset is device size(0) or stripe(1).

Can I suggest that you don't do it like this?  i.e. don't copy the
mistakes I made :-)

I don't think there is any value in supporting multiple near and far copies.
There are two dimensions of the layout:
 - number of copies.  Defaults to 2
 - location of the copies:  near, far, offset

Some day I could implement an alternate version of 'far' or 'offset' which
improves redundancy slightly.
Instead of 
   A B C D
   ...
   D A B C

it would be

   A B C D 
   ....
   B A D C

i.e. treat the devices as pair and swap the device for the second copy.
This doesn't generalise to an odd number of devices, but increases the number
of pairs of devices that can concurrently fail without losing date.
(for 4 devices, there are 6 pairs.  With current 'far' mode there are only 2
pair of devices that can concurrently fail (0,2 and 1,3).  With the proposed
far mode there are 4 (0,2 0,3 1,2, 1,3).

Adding this with your current proposal would be messy.
Adding it with the two dimensions I suggest would simply involve adding
another 'location' - 'farswap' or 'far2' or something.

I note you didn't make 'dm-raid1e' a module alias.  Was that deliberate?

Thanks,
NeilBrown



>   */
>  static int parse_raid_params(struct raid_set *rs, char **argv,
>  			     unsigned num_raid_params)
>  {
> +	unsigned raid10_default = ALGORITHM_RAID10(2, 1, 0);
> +	unsigned raid10_nc = 1, raid10_fc = 1, raid10_fo = 0;
>  	unsigned i, rebuild_cnt = 0;
>  	unsigned long value, region_size = 0;
>  	sector_t sectors_per_dev = rs->ti->len;
> @@ -435,6 +458,7 @@ static int parse_raid_params(struct raid
>  				if (rebuild_cnt > rs->raid_type->parity_devs)
>  					rs->ti->error = "Too many rebuild devices specified for given RAID type";
>  				break;
> +			case 10:
>  			default:
>  				DMERR("The rebuild parameter is not supported for %s", rs->raid_type->name);
>  				rs->ti->error = "Rebuild not supported for this RAID type";
> @@ -492,7 +516,7 @@ static int parse_raid_params(struct raid
>  			 */
>  			value /= 2;
>  
> -			if (rs->raid_type->level < 5) {
> +			if (rs->raid_type->level != 5) {
>  				rs->ti->error = "Inappropriate argument: stripe_cache";
>  				return -EINVAL;
>  			}
> @@ -517,6 +541,33 @@ static int parse_raid_params(struct raid
>  		} else if (!strcasecmp(key, "region_size")) {
>  			rs->print_flags |= DMPF_REGION_SIZE;
>  			region_size = value;
> +		} else if (!strcasecmp(key, "raid10_near_copies") &&
> +			   (rs->raid_type->level == 10)) {
> +			if ((value < 1) || (value > 0xFF)) {
> +				rs->ti->error = "Bad value for 'raid10_near_copies'";
> +				return -EINVAL;
> +			}
> +			rs->print_flags |= DMPF_RAID10_NEAR_COPIES;
> +			raid10_nc = value;
> +			raid10_default = 0;
> +		} else if (!strcasecmp(key, "raid10_far_copies") &&
> +			   (rs->raid_type->level == 10)) {
> +			if ((value < 1) || (value > 0xFF)) {
> +				rs->ti->error = "Bad value for 'raid10_far_copies'";
> +				return -EINVAL;
> +			}
> +			rs->print_flags |= DMPF_RAID10_FAR_COPIES;
> +			raid10_fc = value;
> +			raid10_default = 0;
> +		} else if (!strcasecmp(key, "raid10_far_offset") &&
> +			   (rs->raid_type->level == 10)) {
> +			if (value > 1) {
> +				rs->ti->error = "Bad value for 'raid10_far_offset'";
> +				return -EINVAL;
> +			}
> +			rs->print_flags |= DMPF_RAID10_FAR_OFFSET;
> +			raid10_fo = value;
> +			raid10_default = 0;
>  		} else {
>  			DMERR("Unable to parse RAID parameter: %s", key);
>  			rs->ti->error = "Unable to parse RAID parameters";
> @@ -532,9 +583,33 @@ static int parse_raid_params(struct raid
>  	else
>  		rs->ti->split_io = region_size;
>  
> -	if ((rs->raid_type->level > 1) &&
> -	    sector_div(sectors_per_dev, (rs->md.raid_disks - rs->raid_type->parity_devs))) {
> +	if (rs->raid_type->level == 10) {
> +		/* (Len * Stripes) / Mirrors */
> +		sectors_per_dev *= rs->md.raid_disks;
> +		if (sector_div(sectors_per_dev, (raid10_nc * raid10_fc))) {
> +			rs->ti->error = "Target length not divisible by number of data devices";
> +			return -EINVAL;
> +		}
> +		if ((raid10_nc * raid10_fc) > rs->md.raid_disks) {
> +			rs->ti->error = "Not enough devices to satisfy specification";
> +			return -EINVAL;
> +		}
> +		if (raid10_fo && (raid10_fc < 2)) {
> +			DMWARN("RAID10 parameter 'far_offset' ignored");
> +			raid10_fo = 0;
> +		}
> +
> +		if (raid10_default)
> +			rs->md.layout = raid10_default;
> +		else
> +			rs->md.layout = ALGORITHM_RAID10(raid10_nc,
> +							 raid10_fc, raid10_fo);
> +		rs->md.new_layout = rs->md.layout;
> +	} else if ((rs->raid_type->level > 1) &&
> +		   sector_div(sectors_per_dev,
> +			      (rs->md.raid_disks - rs->raid_type->parity_devs))) {
>  		rs->ti->error = "Target length not divisible by number of data devices";
> +
>  		return -EINVAL;
>  	}
>  	rs->md.dev_sectors = sectors_per_dev;
> @@ -560,6 +635,9 @@ static int raid_is_congested(struct dm_t
>  	if (rs->raid_type->level == 1)
>  		return md_raid1_congested(&rs->md, bits);
>  
> +	if (rs->raid_type->level == 10)
> +		return md_raid10_congested(&rs->md, bits);
> +
>  	return md_raid5_congested(&rs->md, bits);
>  }
>  
> @@ -878,6 +956,9 @@ static int analyse_superblocks(struct dm
>  	case 6:
>  		redundancy = rs->raid_type->parity_devs;
>  		break;
> +	case 10:
> +		redundancy = RAID10_NC(mddev->layout) *	RAID10_FC(mddev->layout);
> +		break;
>  	default:
>  		ti->error = "Unknown RAID type";
>  		return -EINVAL;
> @@ -1197,6 +1278,18 @@ static int raid_status(struct dm_target
>  			DMEMIT(" region_size %lu",
>  			       rs->md.bitmap_info.chunksize >> 9);
>  
> +		if (rs->print_flags & DMPF_RAID10_NEAR_COPIES)
> +			DMEMIT(" raid10_near_copies %u",
> +			       RAID10_NC(rs->md.layout));
> +
> +		if (rs->print_flags & DMPF_RAID10_FAR_COPIES)
> +			DMEMIT(" raid10_far_copies %u",
> +			       RAID10_FC(rs->md.layout));
> +
> +		if (rs->print_flags & DMPF_RAID10_FAR_OFFSET)
> +			DMEMIT(" raid10_far_offset %u",
> +			       RAID10_FO(rs->md.layout));
> +
>  		DMEMIT(" %d", rs->md.raid_disks);
>  		for (i = 0; i < rs->md.raid_disks; i++) {
>  			if (rs->dev[i].meta_dev)
> @@ -1271,7 +1364,7 @@ static void raid_resume(struct dm_target
>  
>  static struct target_type raid_target = {
>  	.name = "raid",
> -	.version = {1, 2, 0},
> +	.version = {1, 3, 0},
>  	.module = THIS_MODULE,
>  	.ctr = raid_ctr,
>  	.dtr = raid_dtr,
> @@ -1298,6 +1391,8 @@ module_init(dm_raid_init);
>  module_exit(dm_raid_exit);
>  
>  MODULE_DESCRIPTION(DM_NAME " raid4/5/6 target");
> +MODULE_ALIAS("dm-raid1");
> +MODULE_ALIAS("dm-raid10");
>  MODULE_ALIAS("dm-raid4");
>  MODULE_ALIAS("dm-raid5");
>  MODULE_ALIAS("dm-raid6");
> Index: linux-upstream/Documentation/device-mapper/dm-raid.txt
> ===================================================================
> --- linux-upstream.orig/Documentation/device-mapper/dm-raid.txt
> +++ linux-upstream/Documentation/device-mapper/dm-raid.txt
> @@ -27,6 +27,11 @@ The target is named "raid" and it accept
>  		- rotating parity N (right-to-left) with data restart
>    raid6_nc	RAID6 N continue
>  		- rotating parity N (right-to-left) with data continuation
> +  raid10/raid1e Various RAID10 inspired algorithms chosen by additional params
> +  		- RAID10: Striped Mirrors (aka 'Striping on top of mirrors')
> +		- RAID1E: Integrated Adjacent Stripe Mirroring
> +		- RAID1E: Integrated Offset Stripe Mirroring
> +		-  and other similar RAID10 variants
>  
>    Reference: Chapter 4 of
>    http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf
> @@ -59,6 +64,80 @@ The target is named "raid" and it accept
>  		logical size of the array.  The bitmap records the device
>  		synchronisation state for each region.
>  
> +        [raid10_near_copies   <# copies>]
> +        [raid10_far_copies    <# copies>]
> +        [raid10_far_offset    <0/1>]
> +		These three options are used to alter the default layout of
> +		a RAID10/RAID1E configuration.  The total number of copies is
> +		given by the number of "near" (aka "adjacent") copies times
> +		the number of "far" (aka "offset") copies.  Near copies
> +		are what most people think of with respect to mirroring.
> +		If 'raid10_near_copies 2', 'raid10_far_copies 1' and
> +		'raid10_far_offset 0', then the layouts for 2, 3 and 4 devices
> +		are:
> +		2 drives         3 drives          4 drives
> +		--------         ----------        --------------
> +		A1  A1           A1  A1  A2        A1  A1  A2  A2
> +		A2  A2           A2  A3  A3        A3  A3  A4  A4
> +		A3  A3           A4  A4  A5        A5  A5  A6  A6
> +		A4  A4           A5  A6  A6        A7  A7  A8  A8
> +		..  ..           ..  ..  ..        ..  ..  ..  ..
> +		The 2-device layout is equivalent 2-way RAID1.  The 4-device
> +		layout is what a traditional RAID10 would look like.  The
> +		3-device layout is what might be called a 'RAID1E - Integrated
> +		Adjacent Stripe Mirroring'.
> +
> +		The 'raid10_far_[copies|offset]' arguments work together to
> +		determine where any "far"/"offset" copies will be placed.
> +		If 'raid10_near_copies 1', 'raid10_far_copies 2' and
> +		'raid10_far_offset 0', then the layouts for 2, 3 and 4 devices
> +		are:
> +		2 drives             3 drives             4 drives
> +		--------             --------------       --------------------
> +		A1  A2               A1   A2   A3         A1   A2   A3   A4
> +		A3  A4               A4   A5   A6         A5   A6   A7   A8
> +		A5  A6               A7   A8   A9         A9   A10  A11  A12
> +		..  ..               ..   ..   ..         ..   ..   ..   ..
> +		A2  A1               A3   A1   A2         A4   A1   A2   A3
> +		A4  A3               A6   A4   A5         A8   A5   A6   A7
> +		A6  A5               A9   A7   A8         A12  A9   A10  A11
> +		..  ..               ..   ..   ..         ..   ..   ..   ..
> +
> +		If 'raid10_near_copies 1', 'raid10_far_copies 2' and
> +		'raid10_far_offset 1', then the layouts for 2, 3 and 4 devices
> +		are:
> +		2 drives       3 drives           4 drives
> +		--------       ------------       -----------------
> +		A1  A2         A1  A2  A3         A1  A2  A3  A4
> +		A2  A1         A3  A1  A2         A4  A1  A2  A3
> +		A3  A4         A4  A5  A6         A5  A6  A7  A8
> +		A4  A3         A6  A4  A5         A8  A5  A6  A7
> +		A5  A6         A7  A8  A9         A9  A10 A11 A12
> +		A6  A5         A9  A7  A8         A12 A9  A10 A11
> +		..  ..         ..  ..  ..         ..  ..  ..  ..
> +		Here we see layouts closely akin to 'RAID1E - Integrated
> +		Offset Stripe Mirroring'.
> +
> +		Near and far copies can both be specified giving more
> +		complex arrangements.  If 'raid10_near_copies 2',
> +		'raid10_far_copies 2' and 'raid10_far_offset 0', then the
> +		layouts for 4 and 5 devices are:
> +		4 drives              5 drives
> +		--------              --------
> +		A1  A1  A2  A2        A1  A1  A2  A2  A3
> +		A3  A3  A4  A4        A3  A4  A4  A5  A5
> +		A5  A5  A6  A6        A6  A6  A7  A7  A8
> +		A7  A7  A8  A8        A8  A9  A9  A10 A10
> +		..  ..  ..  ..        ..  ..  ..  ..  ..
> +		A2  A2  A1  A1        A2  A3  A1  A1  A2
> +		A4  A4  A3  A3        A5  A5  A3  A4  A4
> +		A6  A6  A5  A5        A7  A8  A6  A6  A7
> +		A8  A8  A7  A7        A10 A10 A8  A9  A9
> +		..  ..  ..  ..        ..  ..  ..  ..  ..
> +		Thanks wikipedia 'Non-standard RAID levels' for the layout
> +		figures:
> +		http://en.wikipedia.org/wiki/Non-standard_RAID_levels
> +
>  <#raid_devs>: The number of devices composing the array.
>  	Each device consists of two entries.  The first is the device
>  	containing the metadata (if any); the second is the one containing the
> 

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