Man page updates for new --grow options.
Describe all the new ways that mdadm can reshape arrays. Signed-off-by: NeilBrown <neilb@suse.de>
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NeilBrown
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md.4
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md.4
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@ -584,8 +584,12 @@ array (so the stripes are wider), changing the chunk size (so stripes
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are deeper or shallower), or changing the arrangement of data and
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parity (possibly changing the raid level, e.g. 1 to 5 or 5 to 6).
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As of Linux 2.6.17, md can reshape a raid5 array to have more
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devices. Other possibilities may follow in future kernels.
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As of Linux 2.6.35, md can reshape a RAID4, RAID5, or RAID6 array to
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have a different number of devices (more or fewer) and to have a
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different layout or chunk size. It can also convert between these
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different RAID levels. It can also convert between RAID0 and RAID10,
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and between RAID0 and RAID4 or RAID5.
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Other possibilities may follow in future kernels.
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During any stripe process there is a 'critical section' during which
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live data is being overwritten on disk. For the operation of
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@ -595,6 +599,9 @@ and new number of devices). After this critical section is passed,
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data is only written to areas of the array which no longer hold live
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data \(em the live data has already been located away.
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For a reshape which reduces the number of devices, the 'critical
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section' is at the end of the reshape process.
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md is not able to ensure data preservation if there is a crash
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(e.g. power failure) during the critical section. If md is asked to
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start an array which failed during a critical section of restriping,
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@ -622,8 +629,7 @@ For operations that do not change the size of the array, like simply
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increasing chunk size, or converting RAID5 to RAID6 with one extra
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device, the entire process is the critical section. In this case, the
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restripe will need to progress in stages, as a section is suspended,
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backed up,
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restriped, and released; this is not yet implemented.
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backed up, restriped, and released.
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.SS SYSFS INTERFACE
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Each block device appears as a directory in
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67
mdadm.8.in
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mdadm.8.in
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@ -122,9 +122,10 @@ missing, spare, or failed drives, so there is nothing to monitor.
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.B "Grow"
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Grow (or shrink) an array, or otherwise reshape it in some way.
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Currently supported growth options including changing the active size
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of component devices and changing the number of active devices in RAID
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levels 1/4/5/6, changing the RAID level between 1, 5, and 6, changing
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the chunk size and layout for RAID5 and RAID5, as well as adding or
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of component devices and changing the number of active devices in
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Linear and RAID levels 0/1/4/5/6,
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changing the RAID level between 0, 1, 5, and 6, and between 0 and 10,
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changing the chunk size and layout for RAID 0,4,5,6, as well as adding or
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removing a write-intent bitmap.
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.TP
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@ -900,6 +901,28 @@ not as reliable as you would like.
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.BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
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See this option under Create and Build options.
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.TP
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.BR \-a ", " "\-\-add"
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This option can be used in Grow mode in two cases.
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If the target array is a Linear array, then
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.B \-\-add
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can be used to add one or more devices to the array. They
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are simply catenated on to the end of the array. Once added, the
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devices cannot be removed.
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If the
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.B \-\-raid\-disks
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option is being used to increase the number of devices in an array,
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then
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.B \-\-add
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can be used to add some extra devices to be included in the array.
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In most cases this is not needed as the extra devices can be added as
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spares first, and then the number of raid-disks can be changed.
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However for RAID0, it is not possible to add spares. So to increase
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the number of devices in a RAID0, it is necessary to set the new
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number of devices, and to add the new devices, in the same command.
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.TP
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.BR \-b ", " \-\-bitmap=
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Specify the bitmap file that was given when the array was created. If
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@ -2181,31 +2204,33 @@ and then follow similar steps as above if a matching spare is found.
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The GROW mode is used for changing the size or shape of an active
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array.
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For this to work, the kernel must support the necessary change.
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Various types of growth are being added during 2.6 development,
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including restructuring a RAID5 array to have more active devices.
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Various types of growth are being added during 2.6 development.
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Currently the only support available is to
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Currently the supported changes include
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.IP \(bu 4
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change the "size" attribute
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for RAID1, RAID5 and RAID6.
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change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
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.IP \(bu 4
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increase or decrease the "raid\-devices" attribute of RAID1, RAID5,
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and RAID6.
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increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
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RAID5, and RAID6.
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.IP \bu 4
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change the chunk-size and layout of RAID5 and RAID6.
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change the chunk-size and layout of RAID0, RAID4, RAID5 and RAID6.
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.IP \bu 4
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convert between RAID1 and RAID5, and between RAID5 and RAID6.
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convert between RAID1 and RAID5, between RAID5 and RAID6, between
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RAID0, RAID5, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
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.IP \(bu 4
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add a write-intent bitmap to any array which supports these bitmaps, or
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remove a write-intent bitmap from such an array.
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.PP
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GROW mode is not currently supported for
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.B CONTAINERS
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or arrays inside containers.
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Using GROW on containers is currently only support for Intel's IMSM
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container format. The number of devices in a container can be
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increased - which affects all arrays in the container - or an array
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in a container can be converted between levels where those levels are
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supported by the container, and the conversion is on of those listed
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above.
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.SS SIZE CHANGES
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Normally when an array is built the "size" it taken from the smallest
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Normally when an array is built the "size" is taken from the smallest
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of the drives. If all the small drives in an arrays are, one at a
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time, removed and replaced with larger drives, then you could have an
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array of large drives with only a small amount used. In this
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@ -2244,6 +2269,16 @@ increase the number of devices in a RAID5 safely, including restarting
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an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
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increase or decrease the number of devices in a RAID5 or RAID6.
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From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
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or RAID5.
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.I mdadm
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uses this functionality and the ability to add
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devices to a RAID4 to allow devices to be added to a RAID0. When
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requested to do this,
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.I mdadm
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will convert the RAID0 to a RAID4, add the necessary disks and make
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the reshape happen, and then convert the RAID4 back to RAID0.
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When decreasing the number of devices, the size of the array will also
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decrease. If there was data in the array, it could get destroyed and
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this is not reversible. To help prevent accidents,
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