Veritas VxVM Suite : Vxassist

Petit tutorial sur Veritas VxVM, gestion du raid de VERITAS.

vxassist

General

1. Creating a Volume

1.1 Creating a Concatenated Volume

1.2 Creating a
Striped Volume

1.3 Creating a
RAID-5 Volume

2. Extending a Volume

2.1 Extending a volume up to certain length,

2.2
Extending by a Given Length

3. Shrinking a Volume

3.1
Shrinking to a Given Length

3.2
Shrinking by a Given Length

4. Removing a Volume

5. Mirroring a Volume

5.1 Creating & Mirroring a New Volume

5.2
Mirroring an Existing Volume

5.3 Mirroring
All Volumes

6. Removing a Mirror

7. Adding a RAID-5 Log

8. Adding a DRL Log

9. Removing a RAID-5 Log

10.Preparing a Volume
for Online Backup

11.Displaying
Volume Configuration Information

General

The vxassist utility in Veritas Volume Manager is used to create volumes, add
mirrors and logs to existing volumes, extend and shrink existing volumes,
provides for the migration of data from a specified set of disks, and provides
facilities for the on-line backup of existing volumes.

The default behavior of vxassist is to create volumes in the rootdg diskgroup
if diskgroup is not specified . The default length is taken as number of blocks
but this can be specified in Kilobytes orMegabytes or Gigabytes.

vxassist volume_name [attributes]

Commonly used options are given below (See man vxassist for complete list
of supported options)

-g for specifying diskgroups

-b for background operation

-d file containing defaults for vxassist if not specified /etc/default/vxassist
is used

Keywords used are make , mirror , move , growto ,growby ,shrintto ,shirnkby
,snapstart , snapshot ,snapwait

Attributes specify volumes layout disks controllar to include exclude etc

Default rootdg disk group.

Block Device Node /dev/vx/dsk/volume_name

Raw Device Node /dev/vx/rdsk/volume_name

Other DiskGroups

Block Device Node /dev/vx/dsk/diskgroup_name/volume_name

Raw Device Node /dev/vx/rdsk/diskgroup_name/volume_name

_______________________________________

1. Creating a Volume :

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.

Command syntax :

· 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

To create a striped volume appvol2 100MB striped volume on three specific
disks.

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

1.3 Creating a RAID-5 Volume

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.

Command Syntax :

· vxassist make volume_name
length layout=raid5

To create the RAID-5 volume appvol4 with the default stripe unit size on the
default number of disks with RAID-5 log,

· #vxassist make appvol4 100m
layout=raid5.

2. Extending a Volume

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 .

Command syntax

· vxassist growto volume_name
length

To extend vol3 upto 8000 sectors, type:

· #vxassist growto vol3 8000

2.2 Extending by a Given Length

Command Syntax

· vxassist growby volume_name
length

To extend volapp by 1000 sectors, type:

· #vxassist growby volapp 1000

3. Shrinking a Volume

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

3.2 Shrinking by a Given Length

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

4. Removing a Volume

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

Command Syntax

· vxvol stop volume_name

To stop appvol1

· #vxvol stop appvol1

Command Syntax

· vxedit -rf rm volume_name

To remove the volume appvol1

· #vxedit -rf rm appvol11

5. Mirroring a Volume

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 .

5.1 Creating & Mirroring a New Volume

Command Syntax :

· vxassist make volume_name
length layout=mirror

To create the mirrored volume, appvol22 of 100mb

· #vxassist make appvol22 100m
layout=mirror

To create a volume with Dirty Region Logging enabled

· #vxassist make volume_name
length layout=mirror,log

Command syntax

· vxassist mirror volume_name

Creating a mirror of volume vol44:

· #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

Dirty region logging (DRL) is used with mirrored volume layouts. DRL keeps
track of the regions that have changed due to I/O writes to a mirrored volume.
Prior to every write, a bitmap is written to a log to record the area of the
disk that is being changed. In case of system failure, DRL uses this information
to recover only the portions of the volume that need to be recovered.

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 .

Command Syntax:

• vxassist snapstart volume_name

To create a snapshot mirror of a volume called vol8, type

• #vxassist snapstart vol8

Command Syntax

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

11 Displaying Volume Configuration Information

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

It is assumed that the Veritas software has been installed and that rootdg has been setup by the installer with a minimum of one disk. If not, install the software now.

Use the "format" command to display available disks. If necessary, add new disks to the system and run "drvconfig; devlinks; disks" to configure the new disks. Do not partition disks to be used by Veritas.

To display disks setup for Veritas, use the command "vxdisk list".

To add more disks to the control of Veritas, use the following command:

The would be c2t0d0, for example, without the slice suffix. The vxdiskadd script will prompt for necessary information such as the name of the disk group, whether or not to initialize the new disk, etc. Rerun the command "vxdisk list" to view the new disk.

To designate an unused disk as a hot-spare disk, use the following command:

The would be the Veritas name for the disk, such as disk01. Use "vxdisk list" to confirm that the disk is now a dedicated hot-spare disk. To remove the disk from the dedicated hot-spare pool, use the following command:

By default, Veritas will name disks based on the name of the disk group. To rename a disk (for example, from disk01 to disk02), use the following command:

To place a disk offline (for example, if the disk has become corrupted), run the following command:

The would be c2t0d0, for example, without the slice suffix.

To remove a disk from the diskgroup to which it belongs, run the following command:

To then remove that disk from Veritas control entirely, run the following command:

The same set of commands may be used to move disks from one diskgroup to another:

(For example, "vxdg -g testdg adddisk testdg01=c2t0d0".)

Alternatively, you can simply remove the disk from Veritas control and then reinitialize it with "vxdiskadd". Use "vxdisk list" to confirm the new affiliation.

Every disk group requires a minimum of one disk. The simplest way to add a new diskgroup is to run the "vxdiskadd" command on an unconfigured disk, and when prompted for the name of the diskgroup to use, enter the desired name of the new diskgroup.

To display information on disk groups, run "vxdg list" or "vxdg list".

To destroy a diskgroup and reuse the disks for other purposes, run the following command:

Failing or failed disks can be removed with the "vxdiskadm" menu command. To remove a failing disk, select choice 4, "remove a disk for replacement". To replace the disk later, select choice 5, "replace a failed or removed disk".

The performance of Veritas volumes can be monitored with the "vxstat" command. Reset the volume statistics with the command "vxstat -r", let the system run normally for several hours, and then run "vxstat" and check the read/write performance. If you see two or more heavily used volumes on the same physical disk, you may want to move one of the volumes to an unused disk. To do so, use the following command:

You do not have to specify the new disk name. In that case, the volume will be moved to any available disk. For example, to move the volume called archive from disk03 to disk04, run the following command:

If one volume is particularly heavily used, you may want to convert from the default concatenation to striping. To do so, create a striped plex (mirror) of the volume and then remove the old (concatenated) plex. For example, to convert the volume called archive from concatenated to striped, run the following commands:

The basic command used to create volumes is "vxassist". The format is "vxassist make". The length can be specified in units of kilobytes, megabytes, or gigabytes with the suffixes k, m, or g. By default, new volumes are created from rootdg. Use "-g" to specify a different diskgroup.

To determine the maximum size that a new volume could be given particular attributes, use the "vxassist maxsize" command. For example, to determine the maximum size of a striped volume using disk01 and disk02:

Then create the volume using that length. For example: vxassist make vol01 20g layout=stripe disk01 disk02

By default, the "vxassist" command creates concatenated volumes. For example, the command "vxassist make newvol 10m" would create a concatenated volume with the length of 10 MB. To specify the disk(s) to use, add the disk name(s). For example, "vxassist make newvol 10m disk01".

To create striped volumes, add the attribute "layout=stripe". For exampke, "vxassist make newvol 10g layout=stripe disk01 disk02".

To create RAID-5 volumes, add the attribute "layout=raid5". For example, "vxassist make newvol 30g layout=raid5".

To create mirrored volumes, add the attribute "layout=mirror". For example, "vxassist make newvol 10g layout=mirror".

The "vxassist" command can be used to grow or shrink the size of volumes. Do not shrink the size of volumes below the size of the filesystem. To grow volumes, run one of the following commands:

Similarly, you can shrink the size of volumes:

To remove an unneeded volume, unmount any filesystems on the volume, remove any references to the volume from /etc/vfstab, stop the volume with "vxvol stop", and then run "vxedit -rf rm" or "vxassist remove volume".

Existing volumes can be mirrored to add redundancy. To mirror existing volumes, use the following command:

To remove a mirror (more precisely, to remove one of the plexes from the volume), use the following command:

To stop volumes, use the command "vxvol stop". To stop all volumes, run the command "vxvol stopall". To restart volumes, use the command "vxrecover -s" or use the command Veritas will automatically allocate the necessary space from unused disks. The process may take some time depending on the size of the volume. When fully synchronized, the status of the snapshot mirror will change to SNAPDONE. Use the following command to monitor the progress of the snapshot:

2. Detach the snapshot and create the new read-only snapshot volume with the following command:

The period required to create the snapshot volume is shorter but it is preferred to limit I/O to the volume during the period required.

3. Clean the contents of the new snapshot volume with the following command:

4. Mount the snapshot volume, perform the backup, unmount the volume, and then remove the snapshot volume to save space with the following command:

To remove a volume, unmount any filesystems on the volume and run the following command:

vxassist remove volume

To remove a mirror from a volume (i.e., to remove one of the plexes that belongs to the volume), run the following command:

Any associated subdisks will then become available for other uses. To remove the disk from Volume Manager control entirely, run the following command:

For example, "vxdisk rm c1t1d0s2".

The following techniques can be used to backup mirrored volumes by temporarily taking one of the mirrors offline and then reattaching the mirror to the volume once the backup has been run.

1. Disassociate one of the mirrors from the volume to be backed up:

2. Create a new, temporary volume using the disassociated plex:

3. Start the new volume:

4. Clean the new volume before mounting:

5. Mount the new volume and perform the backup

6. Unmount the new volume

7. Stop the new volume:

8. Disassociate the plex from the new volume:

9. Reattach the plex to the original volume:

10. Delete the temporary volume:

To display the current Veritas configuration, use the following command:

To monitor the progress of tasks, use the following command:

To display information related to plexes, run the following command:

Disk groups can be moved from one system to another with the deport/import commands. The same technique can be used to rename a disk group by deporting the disk group with a new name.

1. Unmount any filesystems on the disk group

2. Stop any volumes on the disk group:

3. Deport the disk group:

4. Import the disk group:

5. Restart and resynchronize the disk group:

6. Remount any filesystems from the disk group

If you have any problems, check the status of volumes on the disk group:

To rename the disk group during deport/import, use the -n argument:

Diskgroups can be moved from one system to another system. On the original system, unmount any volumes in the disk group to be deported and stop them with the command "vxvol stop". Then deport the disk group with the command "vxdg deport".

Move the disks physically to the new system and either reboot the system so that Veritas recognizes the new disks, or use the command "vxdctl enable" to restart vxconfigd.

Import the disks with the command "vxdg import". Then restart all volumes in the disk group with the command "vxrecover -g -sb".

To rename diskgroups during deport/import, run the deport/import command with the argument "-n ". After importing the diskgroup, run the command "vxprint -hrt". The volumes that belong to the imported disk group may be DISABLED. Run the command "vxinfo "volume name" to be sure that the volumes are "startable". Then run "vxrecover -s" to enable each volume.

If the disks in question have been moved due to the crash of the original system, then they will not have been properly deported and will be locked. To unlock the disks, run the command "vxdisk clearimport" or "vxdg -C import". Be sure not to run these commands if the original system has physical access to the disks since that would allow access to the disks from multiple hosts and possibly cause data corruption.