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pvmove can be used to move single LVs by name or multiple LVs that
lie within the specified PV range (e.g. /dev/sdb1:0-1000). When
moving more than one LV, the portions of those LVs that are in the
range to be moved are added to a new temporary pvmove LV. The LVs
then point to the range in the pvmove LV, rather than the PV
range.
Example 1:
We have two LVs in this example. After they were
created, the first LV was grown, yeilding two segments
in LV1. So, there are two LVs with a total of three
segments.
Before pvmove:
--------- --------- ---------
| LV1s0 | | LV2s0 | | LV1s1 |
--------- --------- ---------
| | |
-------------------------------------
PV | 000 - 255 | 256 - 511 | 512 - 767 |
-------------------------------------
After pvmove inserts the temporary pvmove LV:
--------- --------- ---------
| LV1s0 | | LV2s0 | | LV1s1 |
--------- --------- ---------
| | |
-------------------------------------
pvmove0 | seg 0 | seg 1 | seg 2 |
-------------------------------------
| | |
-------------------------------------
PV | 000 - 255 | 256 - 511 | 512 - 767 |
-------------------------------------
Each of the affected LV segments now point to a
range of blocks in the pvmove LV, which purposefully
corresponds to the segments moved from the original
LVs into the temporary pvmove LV.
The current implementation goes on from here to mirror the temporary
pvmove LV by segment. Further, as the pvmove LV is activated, only
one of its segments is actually mirrored (i.e. "moving") at a time.
The rest are either complete or not addressed yet. If the pvmove
is aborted, those segments that are completed will remain on the
destination and those that are not yet addressed or in the process
of moving will stay on the source PV. Thus, it is possible to have
a partially completed move - some LVs (or certain segments of LVs)
on the source PV and some on the destination.
Example 2:
What 'example 1' might look if it was half-way
through the move.
--------- --------- ---------
| LV1s0 | | LV2s0 | | LV1s1 |
--------- --------- ---------
| | |
-------------------------------------
pvmove0 | seg 0 | seg 1 | seg 2 |
-------------------------------------
| | |
| -------------------------
source PV | | 256 - 511 | 512 - 767 |
| -------------------------
| ||
-------------------------
dest PV | 000 - 255 | 256 - 511 |
-------------------------
This update allows the user to specify that they would like the
pvmove mirror created "by LV" rather than "by segment". That is,
the pvmove LV becomes an image in an encapsulating mirror along
with the allocated copy image.
Example 3:
A pvmove that is performed "by LV" rather than "by segment".
--------- ---------
| LV1s0 | | LV2s0 |
--------- ---------
| |
-------------------------
pvmove0 | * LV-level mirror * |
-------------------------
/ \
pvmove_mimage0 / pvmove_mimage1
------------------------- -------------------------
| seg 0 | seg 1 | | seg 0 | seg 1 |
------------------------- -------------------------
| | | |
------------------------- -------------------------
| 000 - 255 | 256 - 511 | | 000 - 255 | 256 - 511 |
------------------------- -------------------------
source PV dest PV
The thing that differentiates a pvmove done in this way and a simple
"up-convert" from linear to mirror is the preservation of the
distinct segments. A normal up-convert would simply allocate the
necessary space with no regard for segment boundaries. The pvmove
operation must preserve the segments because they are the critical
boundary between the segments of the LVs being moved. So, when the
pvmove copy image is allocated, all corresponding segments must be
allocated. The code that merges ajoining segments that are part of
the same LV when the metadata is written must also be avoided in
this case. This method of mirroring is unique enough to warrant its
own definitional macro, MIRROR_BY_SEGMENTED_LV. This joins the two
existing macros: MIRROR_BY_SEG (for original pvmove) and MIRROR_BY_LV
(for user created mirrors).
The advantages of performing pvmove in this way is that all of the
LVs affected can be moved together. It is an all-or-nothing approach
that leaves all LV segments on the source PV if the move is aborted.
Additionally, a mirror log can be used (in the future) to provide tracking
of progress; allowing the copy to continue where it left off in the event
there is a deactivation.
186 lines
6.6 KiB
Groff
186 lines
6.6 KiB
Groff
.TH PVMOVE 8 "LVM TOOLS #VERSION#" "Sistina Software UK" \" -*- nroff -*-
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.SH NAME
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pvmove \(em move physical extents
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.SH SYNOPSIS
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.B pvmove
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.RB [ \-\-abort ]
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.RB [ \-\-alloc
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.IR AllocationPolicy ]
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.RB [ \-\-atomic ]
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.RB [ \-b | \-\-background ]
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.RB [ \-\-commandprofile
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.IR ProfileName ]
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.RB [ \-d | \-\-debug ]
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.RB [ \-h | \-\-help ]
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.RB [ \-i | \-\-interval
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.IR Seconds ]
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.RB [ \-\-noudevsync ]
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.RB [ \-v | \-\-verbose ]
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.RB [ \-n | \-\-name
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.IR LogicalVolume ]
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.RI [ SourcePhysicalVolume [ :PE [ \-PE ]...]
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.RI [ DestinationPhysicalVolume [ :PE [ \-PE ]...]...]]
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.SH DESCRIPTION
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pvmove allows you to move the allocated physical extents (PEs) on
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.I SourcePhysicalVolume
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to one or more other physical volumes (PVs).
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You can optionally specify a source
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.I LogicalVolume
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in which case only extents used by that LV will be moved to
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free (or specified) extents on
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.IR DestinationPhysicalVolume (s).
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If no
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.I DestinationPhysicalVolume
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is specified, the normal allocation rules for the Volume Group are used.
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If pvmove gets interrupted for any reason (e.g. the machine crashes)
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then run pvmove again without any PhysicalVolume arguments to
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restart any moves that were in progress from the last checkpoint.
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Alternatively use \fBpvmove \-\-abort\fP at any time to abort. The
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resulting location of logical volumes after an abort is issued depends
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on whether the
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.B \-\-atomic
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option was used when starting the pvmove process.
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You can run more than one pvmove at once provided they are moving data
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off different SourcePhysicalVolumes, but additional pvmoves will ignore
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any Logical Volumes already in the process of being changed, so some
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data might not get moved.
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\fBpvmove\fP works as follows:
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1. A temporary 'pvmove' Logical Volume is created to store
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details of all the data movements required.
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2. Every Logical Volume in the Volume Group is searched
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for contiguous data that need moving
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according to the command line arguments.
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For each piece of data found, a new segment is added to the end of the
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pvmove LV.
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This segment takes the form of a temporary mirror to copy the data
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from the original location to a newly-allocated location.
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The original LV is updated to use the new temporary mirror segment
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in the pvmove LV instead of accessing the data directly.
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3. The Volume Group metadata is updated on disk.
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4. The first segment of the pvmove Logical Volume is activated and starts
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to mirror the first part of the data. Only one segment is mirrored at once
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as this is usually more efficient.
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5. A daemon repeatedly checks progress at the specified time interval.
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When it detects that the first temporary mirror is in-sync,
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it breaks that mirror so that only the new location for that data gets used
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and writes a checkpoint into the Volume Group metadata on disk.
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Then it activates the mirror for the next segment of the pvmove LV.
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6. When there are no more segments left to be mirrored,
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the temporary Logical Volume is removed and the Volume Group metadata
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is updated so that the Logical Volumes reflect the new data locations.
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Note that this new process cannot support the original LVM1
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type of on-disk metadata. Metadata can be converted using \fBvgconvert\fP(8).
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If the
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.B \-\-atomic
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option is used, a slightly different approach is used for the move. Again,
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a temporary 'pvmove' logical volume is created to store the details of all
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the data movements required. This temporary LV contains all the segments of
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the various LVs that need to be moved. However this time, an identical
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logical volume is allocated that contains the same number of segments and
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a mirror is created to copy the contents from the first temporary LV to the
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second. When a complete copy is accomplished, the temporary logical volumes
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are removed, leaving behind the segments on the destination physical volume.
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If an abort is issued during the move, all logical volumes being moved will
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remain on the source physical volume.
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.SH OPTIONS
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See \fBlvm\fP(8) for common options.
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.TP
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.B \-\-abort
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Abort any moves in progress. If the
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.B \-\-atomic
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option was used to start the pvmove, all logical volumes will remain on
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the source physical volume. Otherwise, those segments that have completed
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the move will stay on the destination physical volume, while those that
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have not will remain on the source physical volume.
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.TP
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.B \-\-atomic
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Make the entire operation atomic. That is, ensure that all affected logical
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volumes are moved to the destination physical volume together; unless the move
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has been aborted. If the move has been aborted, all logical volumes will
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remain on the source physical volume.
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.TP
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.B \-\-noudevsync
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Disable udev synchronisation. The
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process will not wait for notification from udev.
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It will continue irrespective of any possible udev processing
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in the background. You should only use this if udev is not running
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or has rules that ignore the devices LVM2 creates.
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.TP
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.BR \-b ", " \-\-background
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Run the daemon in the background.
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.TP
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.BR \-i ", " \-\-interval " " \fISeconds
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Report progress as a percentage at regular intervals.
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.TP
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.BR \-n ", " \-\-name " " \fILogicalVolume
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Move only the extents belonging to
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.I LogicalVolume
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from
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.I SourcePhysicalVolume
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instead of all allocated extents to the destination physical volume(s).
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.SH Examples
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To move all Physical Extents that are used by simple Logical Volumes on
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/dev/sdb1 to free Physical Extents elsewhere in the Volume Group use:
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.sp
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.B pvmove /dev/sdb1
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.P
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Additionally, a specific destination device /dev/sdc1
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can be specified like this:
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.sp
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.B pvmove /dev/sdb1 /dev/sdc1
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.P
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To perform the action only on extents belonging to the single Logical Volume
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lvol1 do this:
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.sp
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.B pvmove \-n lvol1 /dev/sdb1 /dev/sdc1
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.P
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Rather than moving the contents of the entire device, it is possible to
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move a range of Physical Extents - for example numbers 1000 to 1999
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inclusive on /dev/sdb1 - like this:
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.sp
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.B pvmove /dev/sdb1:1000\-1999
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.P
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A range can also be specified as start+length, so
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.sp
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.B pvmove /dev/sdb1:1000+1000
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.P
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also refers to 1000 Physical Extents starting from Physical Extent number 1000.
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(Counting starts from 0, so this refers to the 1001st to the 2000th inclusive.)
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.P
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To move a range of Physical Extents to a specific location (which must have
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sufficient free extents) use the form:
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.sp
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.B pvmove /dev/sdb1:1000\-1999 /dev/sdc1
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.sp
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or
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.sp
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.B pvmove /dev/sdb1:1000\-1999 /dev/sdc1:0\-999
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.P
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If the source and destination are on the same disk, the
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.B anywhere
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allocation policy would be needed, like this:
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.sp
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.B pvmove \-\-alloc anywhere /dev/sdb1:1000\-1999 /dev/sdb1:0\-999
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.P
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The part of a specific Logical Volume present within in a range of Physical
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Extents can also be picked out and moved, like this:
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.sp
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.B pvmove \-n lvol1 /dev/sdb1:1000\-1999 /dev/sdc1
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.SH SEE ALSO
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.BR lvm (8),
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.BR vgconvert (8)
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.BR pvs (8)
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