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md/raid10: fix the 'new' raid10 layout to work correctly.
In Linux 3.9 we introduce a new 'far' layout for RAID10 which was supposed to rotate the replicas differently and so provide better resilience. In particular it could survive more combinations of 2 drive failures. Unfortunately. due to a coding error, this some did what was wanted, sometimes improved less than we hoped, and sometimes - in very unlikely circumstances - put multiple replicas on the same device so the redundancy was harmed. No public user-space tool has created arrays using this layout so it is very unlikely that zero-redundancy arrays actually exist. Probably no arrays using any form of the new layout exist. But we cannot be certain. So use another bit in the 'layout' number and introduce a bug-fixed version of the layout. Also when assembling an array, if it has a zero-redundancy layout, give a warning. Reported-by: Heinz Mauelshagen <heinzm@redhat.com> Signed-off-by: NeilBrown <neilb@suse.com>
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1 changed files with 20 additions and 2 deletions
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@ -39,6 +39,7 @@
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* far_copies (stored in second byte of layout)
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* far_offset (stored in bit 16 of layout )
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* use_far_sets (stored in bit 17 of layout )
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* use_far_sets_bugfixed (stored in bit 18 of layout )
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*
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* The data to be stored is divided into chunks using chunksize. Each device
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* is divided into far_copies sections. In each section, chunks are laid out
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@ -1497,6 +1498,8 @@ static void status(struct seq_file *seq, struct mddev *mddev)
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seq_printf(seq, " %d offset-copies", conf->geo.far_copies);
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else
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seq_printf(seq, " %d far-copies", conf->geo.far_copies);
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if (conf->geo.far_set_size != conf->geo.raid_disks)
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seq_printf(seq, " %d devices per set", conf->geo.far_set_size);
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}
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seq_printf(seq, " [%d/%d] [", conf->geo.raid_disks,
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conf->geo.raid_disks - mddev->degraded);
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@ -3394,7 +3397,7 @@ static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new)
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disks = mddev->raid_disks + mddev->delta_disks;
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break;
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}
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if (layout >> 18)
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if (layout >> 19)
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return -1;
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if (chunk < (PAGE_SIZE >> 9) ||
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!is_power_of_2(chunk))
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@ -3406,7 +3409,22 @@ static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new)
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geo->near_copies = nc;
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geo->far_copies = fc;
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geo->far_offset = fo;
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geo->far_set_size = (layout & (1<<17)) ? disks / fc : disks;
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switch (layout >> 17) {
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case 0: /* original layout. simple but not always optimal */
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geo->far_set_size = disks;
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break;
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case 1: /* "improved" layout which was buggy. Hopefully no-one is
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* actually using this, but leave code here just in case.*/
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geo->far_set_size = disks/fc;
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WARN(geo->far_set_size < fc,
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"This RAID10 layout does not provide data safety - please backup and create new array\n");
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break;
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case 2: /* "improved" layout fixed to match documentation */
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geo->far_set_size = fc * nc;
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break;
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default: /* Not a valid layout */
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return -1;
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}
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geo->chunk_mask = chunk - 1;
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geo->chunk_shift = ffz(~chunk);
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return nc*fc;
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