_______________________________________

By default, vxassist creates a concatenated volume using the space available on a disk or on the number of disks in a diskgroup if the volume size specified is more then the one available on a single disk.

Disks can be specified from a diskgroup for a volume group but if not mentioned available disks are selected by the volume manager.

· vxassist make volume_name volume_length

To create a new volume appvol of 100 MB in the default disk group rootdg with available disks:

· #vxassist make appvol 100m

To create the volume appvol of 100MB on disk03

· #vxassist make appvol 100m disk03

 

A striped volume contains at least one plex that consists of two or more subdisks located on two or more physical disks.

Command Syntax :

· vxassist make volume_name length layout=stripe

To create a striped volume appvol2 with the default stripe unit size on the default number of disks

· #vxassist make appvol2 100m layout=stripe

· #vxassist make appvol2 100m layout=stripe disk04 disk05 disk06

A RAID-5 volume contains a RAID-5 plex that consists of two or more subdisks located on two or more physical disks. Only one RAID-5 plex can exist per volume. A RAID-5 volume may also contain one or more RAID-5 log plexes, which are used to log information about data and parity being written to the volume.

· vxassist make volume_name length layout=raid5

· #vxassist make appvol4 100m layout=raid5.

Caution : If you plan to use volume size change (grow or shrink ) on a volume with data make sure you have the good backup of the volume available before carrying out such operation .

· vxassist growto volume_name length

· #vxassist growto vol3 8000

· vxassist growby volume_name length

· #vxassist growby volapp 1000

Caution - Do not shrink a volume below the size of the file system. If you have a VxFS file system, you can shrink the file system and then shrink the volume. If you do not shrink the file system first, you risk unrecoverable data loss.

Always make sure you have a good backup of the data volume to be shirnked.

Shrink a volume to a specific length as follows:

· vxassist shrinkto volume_name length

Make sure you do not shrink the volume below the current size of the file system or database using the volume. This command can be safely used on empty volumes.

To shrink volcat to 1300 sectors, type:

· #vxassist shrinkto volcat 1300

Shrink a volume by a specific length as follows:

· vxassist shrinkby volume_name length

To shrink volcat by 8000 sectors, type:

· #vxassist shrinkby volapp2 8000

Removing a volume requires removing all references to the volumes to be removed like unmounting the volume if mounted and removing its reference from /etc/vfstab .

An active volume has to be stopped first to stop all the activities to the volume only then it can be removed 

· vxvol stop volume_name

· #vxvol stop appvol1

· vxedit -rf rm volume_name

· #vxedit -rf rm appvol11

Mirroring allow data to be written simultaneously to two disks so that in case of failure of one disk data is available from the other mirrored disk. Boot disks can be mirriored to provide alternate booting disk .

· vxassist make volume_name length layout=mirror

· #vxassist make appvol22 100m layout=mirror

· #vxassist make volume_name length layout=mirror,log

· vxassist mirror volume_name

· #vxassist mirror vol44

To mirror all existing volumes to available disk space

· /etc/vx/bin/vxmirror -a

Removing a mirror involves first dissociating the plex from its volume and then removing the plex and any associated subdisks completely.The last valid mirror plex associated with a volume cannot be removed.

Dissociate and remove the plex from its volume as follows:

· vxplex -o rm dis plex_name

vxprint -h shows the volume and associated plexes :

To disassociate and remove volmir-02 from volmir, type:

· #vxplex -o rm dis volm-02

The output of vxprint -h for volm now shows volume volm with only one plex::

RAID-5 log plexes are used to log information about data and parity being written to the raid volume. A log plex is created for the volume by default when a raid volume is created but additional ones can be added by following command .

· vxassist addlog name_of_raid5_vol

To put Dirty Region Logging into effect for a volume, a log subdisk must be added to that volume and the volume must be mirrored. Only one log subdisk can exist per plex.

The following example creates a log for the mirrored volume vol03:

· #vxassist addlog vol03

When vxassist is used to add a log subdisk to a volume, a log plex is also created to contain the log subdisk, by default.

Once created, the plex containing a log subdisk can be treated as a regular plex. Data subdisks can be added to the log plex. The log plex and log subdisk can be removed using the same procedures used to remove ordinary plexes and subdisks.

Removing a RAID-5 log involves first dissociating the log from its volume and then removing the log and any associated subdisks completely.

Dissociate the log from its volume as follows:

· #vxplex -o rm dis plex_name

To identify the log plex, use the command:

· vxprint -ht raid5_volume_name

To disassociate the log plex volrd-02 from volrd, type:

· #vxplex -o rm dis volrd-02

 

Disk group: rootdg TY NAME ASSOC KSTATE LENGTH PLOFFS STATE TUTIL0 PUTIL0 v volrd raid5 ENABLED 32 - ACTIVE - - pl volrd-01 volrd ENABLED 32 - ACTIVE - - sd disk01-02 volrd-01 - 32 0 - - - sd disk02-03 volrd-01 - 32 0 - - -

Volume manager provides an easy way to take backup of the online data by creating an offline snapshot mirror of the volume .

The vxassist snapstart operation creates a write-only backup mirror, which is attached to and synchronized with the volume to be backed up and later detached and made offline by vxassist snapshot command . The snapshot volume can be used by backup utilities while the original volume continues to be available for applications and users.

The volume backup method described here does not apply to RAID-5 volumes.

Backing up a volume with vxassist involves the following procedure

snapstart starts creating a online snapshot mirror of the volume using the available disk space . The snapshot is completed with vxassist snapshot command when offline snapshot volume is created with a userdefined name .

• vxassist snapstart volume_name

• #vxassist snapstart vol8

vxassist snapshot volume_name new_volume_name

To create a snapshot volume of vol8, type:

#vxassist snapshot vol8 snapvol8

You can now back up the snapshot volume by whatever means you prefer. To avoid wasting space, you can then remove the snapshot volume, which occupies as much space as the original volume

The vxprint command can be used to display information about how a volume is configured.

Display the volume, mirror, and subdisk record information for all volumes as follows:

  Disk group: rootdg  
  
  DG  NAME        NCONFIG    NLOG      MINORS     GROUP-ID  
  DM  NAME        DEVICE     TYPE      PRIVLEN    PUBLEN     STATE  
  V   NAME        USETYPE    KSTATE    STATE      LENGTH     READPOL      PREFPLEX  
  PL  NAME        VOLUME     KSTATE    STATE      LENGTH     LAYOUT       NCOL/WID MODE  
  SD  NAME        PLEX       DISK      DISKOFFS LENGTH       [COL/]OFF    DEVICE     MODE  
  
  dg  rootdg      759096729.1025.tweety  
  
  dm  disk10      c1t0d0s2 sliced      559        1044400     -  
  dm  disk20      c2t0d0s2 sliced      559        1044400     -  
  
  v   pubs        fsgen      ENABLED ACTIVE       2288       SELECT       -  
  pl  pubs-01     pubs       ENABLED ACTIVE       2288       CONCAT       -          RW  
  sd  disk10-01 pubs-01      disk10    0          2288       0            c0t0d0     ENA  
  
  v   vol8      fsgen      ENABLED ACTIVE       20480      SELECT       -  
  pl  vol8-01   vol8       ENABLED ACTIVE       20480      CONCAT       -          RW  
  sd  disk10-02 vol8-0 disk10        2288       20480      0            c0t1d0     ENA  

where dg is a disk group, dm is a disk, v is a volume, pl is a plex, and sd is a subdisk. The top few lines indicate the headers that match each type of output line that follows. Each volume is listed along with its associated plex(es) and subdisk(s).

Display volume-related information for a specific volume as follows:

#vxprint -t volume_name

To display information about vol8, type:

#vxprint -t vol8

 

Next Steps 

This  article  covered  a very powerful  functionality in veritas volume manager . Veritas manual , lots of  interaction with fellow system administrator and articles like this are the ways to fill in the the gaps  for the lack of many books in this subject . However there are some very good books about the broader  subject matter of storage mangment  

Following are some of the suggested books in this subject .These books are   available for online buying from Amazon.com & provided good knowledge of  backup , storage and high availability .

1. CramSession's Sun Certified Data Management Engineer (emphasis on VERITAS Volume Manager) : Certification Study Guide [DOWNLOAD: PDF]
2. Shared Data Clusters
3. Implementing Backup and Recovery
4. Blueprints for High Availability
5. Designing Storage Area Networks
6. Storage Network Performance Analysis
7. Storage Area Networking Essentials
8. The Backup Book

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