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 | CAUTION: If the existing volume was created before release
3.2 of VxVM, and it has any attached snapshot plexes or it
is associated with any snapshot volumes, follow the procedure given
in “Enabling
Persistent FastResync on Existing Volumes with Associated Snapshots”. The procedure
given in this section is for existing volumes without existing snapshot
plexes or associated snapshot volumes. |
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To put Persistent
FastResync into effect for a volume, a Data Change Object (DCO)
and DCO volume must first be associated with that volume. When you
have added a DCO object and DCO volume to a volume, you can then
enable Persistent FastResync on the volume as described in “Enabling
FastResync on a Volume”.
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 | NOTE: You may need an additional license to use the Persistent
FastResync feature. Even if you do not have a license, you can configure
a DCO object and DCO volume so that snap objects are associated
with the original and snapshot volumes. For more information about
snap objects, see “How
Persistent FastResync Works with Snapshots”. |
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To add a DCO object and DCO volume to an existing volume (which
may already have dirty region logging (DRL) enabled), use the following procedure:
Ensure that the disk group containing the
existing volume has been upgraded to at least version 90. Use the
following command to check the version of a disk group:
# vxdg list diskgroup
To upgrade a disk group to the latest version, use the following command:
# vxdg upgrade diskgroup
For more information, see “Upgrading
a Disk Group”.
Use the following command to turn off Non-Persistent
FastResync on the original volume if it is currently enabled:
# vxvol [-g diskgroup] set fastresync=off volume
If you are uncertain about which volumes have Non-Persistent FastResync
enabled, use the following command to obtain a listing of such volumes:
# vxprint [-g diskgroup] -F “%name” \
-e “v_fastresync=on && !v_hasdcolog”
Use the following command to add a DCO and DCO volume
to the existing volume:
# vxassist [-g diskgroup[ addlog volume logtype=dco \
[ndcomirror=number] [dcolen=size] [storage_attributes]
For non-layered volumes, the default number of plexes in the
mirrored DCO volume is equal to the lesser of the number of plexes
in the data volume or 2. For layered volumes, the default number
of DCO plexes is always 2. If required, use the ndcomirror
attribute to specify a different number. It is recommended that
you configure as many DCO plexes as there are existing data and
snapshot plexes in the volume. For example, specify ndcomirror=3
when adding a DCO to a 3-way mirrored volume.
The default size of each plex is 132 blocks. You can use the dcolen attribute
to specify a different size. If specified, the size of the plex
must be a integer multiple of 33 blocks from 33 up to a maximum
of 2112 blocks.
To view the details of the DCO object and DCO volume that
are associated with a volume, use the vxprint command. The following
is example vxprint
output for the volume named zoo (the TUTIL0 and PUTIL0 columns are
omitted for clarity):
TY NAME ASSOC KSTATE LENGTH PLOFFS STATE ...
v zoo fsgen ENABLED 1024 - ACTIVE
pl zoo-01 zoo ENABLED 1024 - ACTIVE
sd c1t66d0-02 zoo-01 ENABLED 1024 0 -
pl foo-02 zoo ENABLED 1024 - ACTIVE
sd c1t67d0-02 zoo-02 ENABLED 1024 0 -
dc zoo_dco zoo - - - -
v zoo_dcl gen ENABLED 132 - ACTIVE
pl zoo_dcl-01 zoo_dcl ENABLED 132 - ACTIVE
sd c1t66d0-01 zoo_dcl-01 ENABLED 132 0 -
pl zoo_dcl-02 zoo_dcl ENABLED 132 - ACTIVE
sd c1t67d0-01 zoo_dcl-02 ENABLED 132 0 -
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In this output, the DCO object is shown as zoo_dco, and the
DCO volume as zoo_dcl with 2 plexes, zoo_dcl-01 and zoo_dcl-02.
For more information, see the vxassist(1M) manual page.
Specifying
Storage for DCO Plexes |
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If
the disks that contain volumes and their snapshots are to be moved
or split into different disk groups, the disks that contain their
respective DCO plexes must be able to accompany them. By default, VxVM attempts
to place the DCO plexes on the same disks as the data plexes of the
parent volume. However, this may be impossible if there is insufficient
space available on those disks. In this case, VxVM uses any available
space on other disks in the disk group. If the DCO plexes are placed
on disks which are used to hold the plexes of other volumes, this may
cause problems when you subsequently attempt to move volumes into
other disk groups.
You can use storage attributes to specify explicitly which
disks to use for the DCO plexes. If possible, specify the same disks
as those on which the volume is configured. For example, to add
a DCO object and DCO volume with plexes on disk5 and disk6, and
a plex size of 264 blocks to the volume, myvol, use the following
command:
# vxassist -g mydg addlog myvol logtype=dco dcolen=264 \ disk5 disk6
If required, you can use
the vxassist move command to relocate DCO plexes to different disks.
For example, the following command moves the plexes of the DCO volume
for volume vol1 from disk3 and disk4 to disk7 and disk8:
# vxassist -g mydg move vol1_dcl !disk4 disk7 disk8
For more information, see “Considerations
for Placing DCO Plexes”.
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