Re: [PATCH 4 of 4 - v2] DM RAID: Add support for MD's RAID10 "far" and "offset" algorithms

[NeilBrown <neilb@suse.de>]

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On Mon, 07 Jan 2013 16:09:41 -0600 Jonathan Brassow <jbrassow@redhat.com>
wrote:

> DM RAID:  Add support for MD's RAID10 "far" and "offset" algorithms
> 
> Until now, dm-raid.c only supported the "near" algorthm of MD's RAID10
> implementation.  This patch adds support for the "far" and "offset"
> algorithms, but only with the improved redundancy that is brought with
> the introduction of the 'use_far_sets' bit, which shifts copied stripes
> according to smaller sets vs the entire array.  That is, the 17th bit
> of the 'layout' variable that defines the RAID10 implementation will
> always be set.   (More information on how the 'layout' variable selects
> the RAID10 algorithm can be found in the opening comments of
> drivers/md/raid10.c.)
> 
> Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>

Applied, pushed out on my for-next branch.
Thanks,
NeilBrown


> 
> 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
> @@ -30,6 +30,7 @@ The target is named "raid" and it accept
>    raid10        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
> @@ -64,15 +65,15 @@ The target is named "raid" and it accept
>  		synchronisation state for each region.
>  
>          [raid10_copies   <# copies>]
> -        [raid10_format   near]
> +        [raid10_format   <near|far|offset>]
>  		These two options are used to alter the default layout of
>  		a RAID10 configuration.  The number of copies is can be
> -		specified, but the default is 2.  There are other variations
> -		to how the copies are laid down - the default and only current
> -		option is "near".  Near copies are what most people think of
> -		with respect to mirroring.  If these options are left
> -		unspecified, or 'raid10_copies 2' and/or 'raid10_format near'
> -		are given, then the layouts for 2, 3 and 4 devices are:
> +		specified, but the default is 2.  There are also three
> +		variations to how the copies are laid down - the default
> +		is "near".  Near copies are what most people think of with
> +		respect to mirroring.  If these options are left unspecified,
> +		or 'raid10_copies 2' and/or 'raid10_format near' are given,
> +		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
> @@ -85,6 +86,33 @@ The target is named "raid" and it accept
>  		3-device layout is what might be called a 'RAID1E - Integrated
>  		Adjacent Stripe Mirroring'.
>  
> +		If 'raid10_copies 2' and 'raid10_format far', 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         A2   A1   A4   A3
> +		A4  A3               A6   A4   A5         A6   A5   A8   A7
> +		A6  A5               A9   A7   A8         A10  A9   A12  A11
> +		..  ..               ..   ..   ..         ..   ..   ..   ..
> +
> +		If 'raid10_copies 2' and 'raid10_format offset', 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         A2  A1  A4  A3
> +		A3  A4         A4  A5  A6         A5  A6  A7  A8
> +		A4  A3         A6  A4  A5         A6  A5  A8  A7
> +		A5  A6         A7  A8  A9         A9  A10 A11 A12
> +		A6  A5         A9  A7  A8         A10 A9  A12 A11
> +		..  ..         ..  ..  ..         ..  ..  ..  ..
> +		Here we see layouts closely akin to 'RAID1E - Integrated
> +		Offset Stripe Mirroring'.
> +
>  <#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
> @@ -141,3 +169,5 @@ Version History
>  1.2.0	Handle creation of arrays that contain failed devices.
>  1.3.0	Added support for RAID 10
>  1.3.1	Allow device replacement/rebuild for RAID 10
> +1.4.0	Non-functional change.  Removes arg from mapping function.
> +1.4.1   Add RAID10 "far" and "offset" algorithm support.
> Index: linux-upstream/drivers/md/dm-raid.c
> ===================================================================
> --- linux-upstream.orig/drivers/md/dm-raid.c
> +++ linux-upstream/drivers/md/dm-raid.c
> @@ -91,15 +91,44 @@ static struct raid_type {
>  	{"raid6_nc", "RAID6 (N continue)",		2, 4, 6, ALGORITHM_ROTATING_N_CONTINUE}
>  };
>  
> +static char *raid10_md_layout_to_format(int layout)
> +{
> +	/*
> +	 * Bit 16 and 17 stand for "offset" and "use_far_sets"
> +	 * Refer to MD's raid10.c for details
> +	 */
> +	if ((layout & 0x10000) && (layout & 0x20000))
> +		return "offset";
> +
> +	if ((layout & 0xFF) > 1)
> +		return "near";
> +
> +	return "far";
> +}
> +
>  static unsigned raid10_md_layout_to_copies(int layout)
>  {
> -	return layout & 0xFF;
> +	if ((layout & 0xFF) > 1)
> +		return layout & 0xFF;
> +	return (layout >> 8) & 0xFF;
>  }
>  
>  static int raid10_format_to_md_layout(char *format, unsigned copies)
>  {
> -	/* 1 "far" copy, and 'copies' "near" copies */
> -	return (1 << 8) | (copies & 0xFF);
> +	unsigned n = 1, f = 1;
> +
> +	if (!strcmp("near", format))
> +		n = copies;
> +	else
> +		f = copies;
> +
> +	if (!strcmp("offset", format))
> +		return 0x30000 | (f << 8) | n;
> +
> +	if (!strcmp("far", format))
> +		return 0x20000 | (f << 8) | n;
> +
> +	return (f << 8) | n;
>  }
>  
>  static struct raid_type *get_raid_type(char *name)
> @@ -352,6 +381,7 @@ static int validate_rebuild_devices(stru
>  {
>  	unsigned i, rebuild_cnt = 0;
>  	unsigned rebuilds_per_group, copies, d;
> +	unsigned group_size, last_group_start;
>  
>  	if (!(rs->print_flags & DMPF_REBUILD))
>  		return 0;
> @@ -381,9 +411,6 @@ static int validate_rebuild_devices(stru
>  		 * as long as the failed devices occur in different mirror
>  		 * groups (i.e. different stripes).
>  		 *
> -		 * Right now, we only allow for "near" copies.  When other
> -		 * formats are added, we will have to check those too.
> -		 *
>  		 * When checking "near" format, make sure no adjacent devices
>  		 * have failed beyond what can be handled.  In addition to the
>  		 * simple case where the number of devices is a multiple of the
> @@ -394,13 +421,39 @@ static int validate_rebuild_devices(stru
>  		 *          C    D    D    E    E
>  		 */
>  		rebuilds_per_group = 0;
> -		for (i = 0; i < rs->md.raid_disks * copies; i++) {
> -			d = i % rs->md.raid_disks;
> -			if (!test_bit(In_sync, &rs->dev[d].rdev.flags) &&
> -			    (++rebuilds_per_group >= copies))
> -				goto too_many;
> -			if (!((i + 1) % copies))
> +		if (!strcmp("near", raid10_md_layout_to_format(rs->md.layout))) {
> +			for (i = 0; i < rs->md.raid_disks * copies; i++) {
> +				d = i % rs->md.raid_disks;
> +				if (!test_bit(In_sync, &rs->dev[d].rdev.flags) &&
> +				    (++rebuilds_per_group >= copies))
> +					goto too_many;
> +				if (!((i + 1) % copies))
> +					rebuilds_per_group = 0;
> +			}
> +			break;
> +		}
> +
> +		/*
> +		 * When checking "far" and "offset" formats, we need to ensure
> +		 * that the device that holds its copy is not also dead or
> +		 * being rebuilt.  (Note that "far" and "offset" formats only
> +		 * support two copies right now.  These formats also only ever
> +		 * use the 'use_far_sets' variant.)
> +		 *
> +		 * This check is somewhat complicated by the need to account
> +		 * for arrays that are not a multiple of (far) copies.  This
> +		 * results in the need to treat the last (potentially larger)
> +		 * set differently.
> +		 */
> +		group_size = (rs->md.raid_disks / copies);
> +		last_group_start = (rs->md.raid_disks / group_size) - 1;
> +		last_group_start *= group_size;
> +		for (i = 0; i < rs->md.raid_disks; i++) {
> +			if (!(i % copies) && !(i > last_group_start))
>  				rebuilds_per_group = 0;
> +			if (!test_bit(In_sync, &rs->dev[i].rdev.flags) &&
> +			    (++rebuilds_per_group >= copies))
> +					goto too_many;
>  		}
>  		break;
>  	default:
> @@ -438,7 +491,7 @@ too_many:
>   *
>   * RAID10-only options:
>   *    [raid10_copies <# copies>]        Number of copies.  (Default: 2)
> - *    [raid10_format <near>]            Layout algorithm.  (Default: near)
> + *    [raid10_format <near|far|offset>] Layout algorithm.  (Default: near)
>   */
>  static int parse_raid_params(struct raid_set *rs, char **argv,
>  			     unsigned num_raid_params)
> @@ -525,7 +578,9 @@ static int parse_raid_params(struct raid
>  				rs->ti->error = "'raid10_format' is an invalid parameter for this RAID type";
>  				return -EINVAL;
>  			}
> -			if (strcmp("near", argv[i])) {
> +			if (strcmp("near", argv[i]) &&
> +			    strcmp("far", argv[i]) &&
> +			    strcmp("offset", argv[i])) {
>  				rs->ti->error = "Invalid 'raid10_format' value given";
>  				return -EINVAL;
>  			}
> @@ -649,6 +704,15 @@ static int parse_raid_params(struct raid
>  			return -EINVAL;
>  		}
>  
> +		/*
> +		 * If the format is not "near", we only support
> +		 * two copies at the moment.
> +		 */
> +		if (strcmp("near", raid10_format) && (raid10_copies > 2)) {
> +			rs->ti->error = "Too many copies for given RAID10 format.";
> +			return -EINVAL;
> +		}
> +
>  		/* (Len * #mirrors) / #devices */
>  		sectors_per_dev = rs->ti->len * raid10_copies;
>  		sector_div(sectors_per_dev, rs->md.raid_disks);
> @@ -862,17 +926,30 @@ static int super_init_validation(struct
>  	/*
>  	 * Reshaping is not currently allowed
>  	 */
> -	if ((le32_to_cpu(sb->level) != mddev->level) ||
> -	    (le32_to_cpu(sb->layout) != mddev->layout) ||
> -	    (le32_to_cpu(sb->stripe_sectors) != mddev->chunk_sectors)) {
> -		DMERR("Reshaping arrays not yet supported.");
> +	if (le32_to_cpu(sb->level) != mddev->level) {
> +		DMERR("Reshaping arrays not yet supported. (RAID level change)");
> +		return -EINVAL;
> +	}
> +	if (le32_to_cpu(sb->layout) != mddev->layout) {
> +		DMERR("Reshaping arrays not yet supported. (RAID layout change)");
> +		DMERR("  0x%X vs 0x%X", le32_to_cpu(sb->layout), mddev->layout);
> +		DMERR("  Old layout: %s w/ %d copies",
> +		      raid10_md_layout_to_format(le32_to_cpu(sb->layout)),
> +		      raid10_md_layout_to_copies(le32_to_cpu(sb->layout)));
> +		DMERR("  New layout: %s w/ %d copies",
> +		      raid10_md_layout_to_format(mddev->layout),
> +		      raid10_md_layout_to_copies(mddev->layout));
> +		return -EINVAL;
> +	}
> +	if (le32_to_cpu(sb->stripe_sectors) != mddev->chunk_sectors) {
> +		DMERR("Reshaping arrays not yet supported. (stripe sectors change)");
>  		return -EINVAL;
>  	}
>  
>  	/* We can only change the number of devices in RAID1 right now */
>  	if ((rs->raid_type->level != 1) &&
>  	    (le32_to_cpu(sb->num_devices) != mddev->raid_disks)) {
> -		DMERR("Reshaping arrays not yet supported.");
> +		DMERR("Reshaping arrays not yet supported. (device count change)");
>  		return -EINVAL;
>  	}
>  
> @@ -1356,7 +1433,8 @@ static int raid_status(struct dm_target
>  			       raid10_md_layout_to_copies(rs->md.layout));
>  
>  		if (rs->print_flags & DMPF_RAID10_FORMAT)
> -			DMEMIT(" raid10_format near");
> +			DMEMIT(" raid10_format %s",
> +			       raid10_md_layout_to_format(rs->md.layout));
>  
>  		DMEMIT(" %d", rs->md.raid_disks);
>  		for (i = 0; i < rs->md.raid_disks; i++) {
> @@ -1432,7 +1510,7 @@ static void raid_resume(struct dm_target
>  
>  static struct target_type raid_target = {
>  	.name = "raid",
> -	.version = {1, 4, 0},
> +	.version = {1, 4, 1},
>  	.module = THIS_MODULE,
>  	.ctr = raid_ctr,
>  	.dtr = raid_dtr,
> @@ -1447,6 +1525,10 @@ static struct target_type raid_target =
>  
>  static int __init dm_raid_init(void)
>  {
> +	DMINFO("Loading target version %u.%u.%u",
> +	       raid_target.version[0],
> +	       raid_target.version[1],
> +	       raid_target.version[2]);
>  	return dm_register_target(&raid_target);
>  }
>  
> 


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