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Diffstat (limited to 'Documentation/admin-guide/device-mapper/dm-raid.rst')
| -rw-r--r-- | Documentation/admin-guide/device-mapper/dm-raid.rst | 80 |
1 files changed, 73 insertions, 7 deletions
diff --git a/Documentation/admin-guide/device-mapper/dm-raid.rst b/Documentation/admin-guide/device-mapper/dm-raid.rst index bb17e26e3c1b..e11f10764770 100644 --- a/Documentation/admin-guide/device-mapper/dm-raid.rst +++ b/Documentation/admin-guide/device-mapper/dm-raid.rst @@ -20,10 +20,10 @@ The target is named "raid" and it accepts the following parameters:: raid0 RAID0 striping (no resilience) raid1 RAID1 mirroring raid4 RAID4 with dedicated last parity disk - raid5_n RAID5 with dedicated last parity disk supporting takeover + raid5_n RAID5 with dedicated last parity disk supporting takeover from/to raid1 Same as raid4 - - Transitory layout + - Transitory layout for takeover from/to raid1 raid5_la RAID5 left asymmetric - rotating parity 0 with data continuation @@ -48,8 +48,8 @@ The target is named "raid" and it accepts the following parameters:: raid6_n_6 RAID6 with dedicate parity disks - parity and Q-syndrome on the last 2 disks; - layout for takeover from/to raid4/raid5_n - raid6_la_6 Same as "raid_la" plus dedicated last Q-syndrome disk + layout for takeover from/to raid0/raid4/raid5_n + raid6_la_6 Same as "raid_la" plus dedicated last Q-syndrome disk supporting takeover from/to raid5 - layout for takeover from raid5_la from/to raid6 raid6_ra_6 Same as "raid5_ra" dedicated last Q-syndrome disk @@ -173,9 +173,9 @@ The target is named "raid" and it accepts the following parameters:: The delta_disks option value (-251 < N < +251) triggers device removal (negative value) or device addition (positive value) to any reshape supporting raid levels 4/5/6 and 10. - RAID levels 4/5/6 allow for addition of devices (metadata - and data device tuple), raid10_near and raid10_offset only - allow for device addition. raid10_far does not support any + RAID levels 4/5/6 allow for addition and removal of devices + (metadata and data device tuple), raid10_near and raid10_offset + only allow for device addition. raid10_far does not support any reshaping at all. A minimum of devices have to be kept to enforce resilience, which is 3 devices for raid4/5 and 4 devices for raid6. @@ -372,6 +372,72 @@ to safely enable discard support for RAID 4/5/6: 'devices_handle_discards_safely' +Takeover/Reshape Support +------------------------ +The target natively supports these two types of MDRAID conversions: + +o Takeover: Converts an array from one RAID level to another + +o Reshape: Changes the internal layout while maintaining the current RAID level + +Each operation is only valid under specific constraints imposed by the existing array's layout and configuration. + + +Takeover: +linear -> raid1 with N >= 2 mirrors +raid0 -> raid4 (add dedicated parity device) +raid0 -> raid5 (add dedicated parity device) +raid0 -> raid10 with near layout and N >= 2 mirror groups (raid0 stripes have to become first member within mirror groups) +raid1 -> linear +raid1 -> raid5 with 2 mirrors +raid4 -> raid5 w/ rotating parity +raid5 with dedicated parity device -> raid4 +raid5 -> raid6 (with dedicated Q-syndrome) +raid6 (with dedicated Q-syndrome) -> raid5 +raid10 with near layout and even number of disks -> raid0 (select any in-sync device from each mirror group) + +Reshape: +linear: not possible +raid0: not possible +raid1: change number of mirrors +raid4: add and remove stripes (minimum 3), change stripesize +raid5: add and remove stripes (minimum 3, special case 2 for raid1 takeover), change rotating parity algorithms, change stripesize +raid6: add and remove stripes (minimum 4), change rotating syndrome algorithms, change stripesize +raid10 near: add stripes (minimum 4), change stripesize, no stripe removal possible, change to offset layout +raid10 offset: add stripes, change stripesize, no stripe removal possible, change to near layout +raid10 far: not possible + +Table line examples: + +### raid1 -> raid5 +# +# 2 devices limitation in raid1. +# raid5 personality is able to just map 2 like raid1. +# Reshape after takeover to change to full raid5 layout + + 0 1960886272 raid raid1 3 0 region_size 2048 2 /dev/dm-0 /dev/dm-1 /dev/dm-2 /dev/dm-3 + +# dm-0 and dm-2 are e.g. 4MiB large metadata devices, dm-1 and dm-3 have to be at least 1960886272 big. +# +# Table line to takeover to raid5 + + 0 1960886272 raid raid5 3 0 region_size 2048 2 /dev/dm-0 /dev/dm-1 /dev/dm-2 /dev/dm-3 + +# Add required out-of-place reshape space to the beginniong of the given 2 data devices, +# allocate another metadata/data device tuple with the same sizes for the parity space +# and zero the first 4K of the metadata device. +# +# Example table of the out-of-place reshape space addition for one data device, e.g. dm-1 + + 0 8192 linear 8:0 0 1960903888 # <- must be free space segment + 8192 1960886272 linear 8:0 0 2048 # previous data segment + +# Mapping table for e.g. raid5_rs reshape causing the size of the raid device to double-fold once the reshape finishes. +# Check the status output (e.g. "dmsetup status $RaidDev") for progess. + + 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 + + Version History --------------- |