dm raid: add documentation for takeover/reshape raid1 -> raid5 table line examples
Also enhance possible takeover/reshape information and do some reformatting. Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>master
Heinz Mauelshagen
Mikulas Patocka
parent
ab08f9c8b3
commit
7799eaecfe
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@ -20,10 +20,10 @@ The target is named "raid" and it accepts the following parameters::
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raid0 RAID0 striping (no resilience)
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raid1 RAID1 mirroring
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raid4 RAID4 with dedicated last parity disk
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raid5_n RAID5 with dedicated last parity disk supporting takeover
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raid5_n RAID5 with dedicated last parity disk supporting takeover from/to raid1
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Same as raid4
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- Transitory layout
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- Transitory layout for takeover from/to raid1
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raid5_la RAID5 left asymmetric
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- rotating parity 0 with data continuation
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@ -48,8 +48,8 @@ The target is named "raid" and it accepts the following parameters::
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raid6_n_6 RAID6 with dedicate parity disks
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- parity and Q-syndrome on the last 2 disks;
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layout for takeover from/to raid4/raid5_n
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raid6_la_6 Same as "raid_la" plus dedicated last Q-syndrome disk
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layout for takeover from/to raid0/raid4/raid5_n
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raid6_la_6 Same as "raid_la" plus dedicated last Q-syndrome disk supporting takeover from/to raid5
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- layout for takeover from raid5_la from/to raid6
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raid6_ra_6 Same as "raid5_ra" dedicated last Q-syndrome disk
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@ -173,9 +173,9 @@ The target is named "raid" and it accepts the following parameters::
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The delta_disks option value (-251 < N < +251) triggers
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device removal (negative value) or device addition (positive
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value) to any reshape supporting raid levels 4/5/6 and 10.
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RAID levels 4/5/6 allow for addition of devices (metadata
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and data device tuple), raid10_near and raid10_offset only
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allow for device addition. raid10_far does not support any
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RAID levels 4/5/6 allow for addition and removal of devices
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(metadata and data device tuple), raid10_near and raid10_offset
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only allow for device addition. raid10_far does not support any
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reshaping at all.
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A minimum of devices have to be kept to enforce resilience,
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which is 3 devices for raid4/5 and 4 devices for raid6.
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@ -372,6 +372,72 @@ to safely enable discard support for RAID 4/5/6:
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'devices_handle_discards_safely'
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Takeover/Reshape Support
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------------------------
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The target natively supports these two types of MDRAID conversions:
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o Takeover: Converts an array from one RAID level to another
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o Reshape: Changes the internal layout while maintaining the current RAID level
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Each operation is only valid under specific constraints imposed by the existing array's layout and configuration.
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Takeover:
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linear -> raid1 with N >= 2 mirrors
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raid0 -> raid4 (add dedicated parity device)
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raid0 -> raid5 (add dedicated parity device)
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raid0 -> raid10 with near layout and N >= 2 mirror groups (raid0 stripes have to become first member within mirror groups)
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raid1 -> linear
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raid1 -> raid5 with 2 mirrors
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raid4 -> raid5 w/ rotating parity
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raid5 with dedicated parity device -> raid4
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raid5 -> raid6 (with dedicated Q-syndrome)
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raid6 (with dedicated Q-syndrome) -> raid5
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raid10 with near layout and even number of disks -> raid0 (select any in-sync device from each mirror group)
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Reshape:
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linear: not possible
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raid0: not possible
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raid1: change number of mirrors
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raid4: add and remove stripes (minimum 3), change stripesize
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raid5: add and remove stripes (minimum 3, special case 2 for raid1 takeover), change rotating parity algorithms, change stripesize
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raid6: add and remove stripes (minimum 4), change rotating syndrome algorithms, change stripesize
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raid10 near: add stripes (minimum 4), change stripesize, no stripe removal possible, change to offset layout
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raid10 offset: add stripes, change stripesize, no stripe removal possible, change to near layout
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raid10 far: not possible
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Table line examples:
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### raid1 -> raid5
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#
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# 2 devices limitation in raid1.
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# raid5 personality is able to just map 2 like raid1.
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# Reshape after takeover to change to full raid5 layout
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0 1960886272 raid raid1 3 0 region_size 2048 2 /dev/dm-0 /dev/dm-1 /dev/dm-2 /dev/dm-3
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# dm-0 and dm-2 are e.g. 4MiB large metadata devices, dm-1 and dm-3 have to be at least 1960886272 big.
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#
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# Table line to takeover to raid5
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0 1960886272 raid raid5 3 0 region_size 2048 2 /dev/dm-0 /dev/dm-1 /dev/dm-2 /dev/dm-3
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# Add required out-of-place reshape space to the beginniong of the given 2 data devices,
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# allocate another metadata/data device tuple with the same sizes for the parity space
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# and zero the first 4K of the metadata device.
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#
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# Example table of the out-of-place reshape space addition for one data device, e.g. dm-1
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0 8192 linear 8:0 0 1960903888 # <- must be free space segment
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8192 1960886272 linear 8:0 0 2048 # previous data segment
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# Mapping table for e.g. raid5_rs reshape causing the size of the raid device to double-fold once the reshape finishes.
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# Check the status output (e.g. "dmsetup status $RaidDev") for progess.
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0 $((2 * 1960886272)) raid raid5 7 0 region_size 2048 data_offset 8192 delta_disk 1 2 /dev/dm-0 /dev/dm-1 /dev/dm-2 /dev/dm-3
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Version History
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---------------
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