Vxdiskadm

[Kayleen]

Themain features of volume manager are following

1. Allows creation of logical volumes spanning over multiple disks. This overcomes the physical limit of the disk .

2. Provides high availability storage solutions through RAID ,Mirroring of disks .

3. Provides fail over features by providing transferable disk group ownership between systems.

4. Dynamic reconfiguration of disk storage in an online system state. what is veritas volume manager .

For example device name c2t3d0s2 represents controller number 2 , target id 3 , disk group 0 and slice 2 and disk01 may be its disk name . While device name is system dependent based on controller and disk id the disk name is user defined .

Disk groups

* A disk group is a collection of volume manager disks grouped together to hold the data . All the configuration changes made to a disk group are applied to the disks in that disk group only.

* Volume Manager objects cannot span disk groups i.e. all the operations on a particular disk group remains confined to that particular group .

* Disk groups enable high availability as these can be shared by two or more hosts but can be accessed by only one host at a time. In two hosts and a shared storage situation one host can take over the ownership of the disk groups and drives in case other host fails.

Volume Manager disks

* Adding physical disks to the volume manager results in creation of public and private region in the disk by the volume manager .The public region is the disk space available for volume space and the private region stores the configuration information.

* A Volume Manager disks are created from the public region of a physical disk that is under Volume Manager control. Each volume manager disk corresponds to one physical disk.

* A volume manager disk is given a disk media name when it is added to a disk group which can be default or unique user defined..

* Once a volume manager disk is assigned a disk media name, the disk is no longer referred to by its physical address of c#t#d#. The physical address of c#t#d# becomes known as the disk access record.

A subdisk is similar to a partition but with following differences :

* The maximum number of partitions to a disk is eight.

* There is no theoretical limit to number of subdisks that can be attached to a single plex, but it has been limited to a default value of 4096. If required, this default can be changed, using the vol_subdisk_num tunable parameter.

Volume configuration consists of adding two or more disks to form disk group and create volume/s from this disk group. File system can be created on these volumes or these can be accessed as raw devices for some database applications. First step in volume manager configuration consists of adding and initializing disks under volume manager which creates a public region which is bulk of disk space available for volume space .Private region which is generally of a few megabytes stores the disk configuration information .

By default all the available disks in the system are considered for inclusion as volume manager disk however to exclude certain disks, list the names of the disks to be excluded in the file /etc/vx/disks.exclude before the initialization or encapsulation. Similarly, you can exclude all disks on specific controllers from initialization or encapsulation by listing those controllers in the file /etc/vx/cntrls.exclude.

The formatted disks can be added or initialized with volume manager . Disk groups needs to be given for making a new group or adding disks in existing group. Default disk group is rootdg and if none is specified the disks are added to volume manager and are kept as hot spares which can be used in place of a failed disk.

Use this operation to add one or more disks to a disk group. You can add the selected disks to an existing disk group or to a new disk group that will be created as a part of the operation. The selected disks may also be added to a disk group as spares. The selected disks may also be initialized without adding them to a disk group leaving the disks available for use as replacement disks.

All disks attached to the system are recognized by the Volume Manager and displayed here.. Error status indicates disks not recognized by volume manager as part of volume manager and can be used to add in the volume manager .. Disks with a name , group and online status are present in volume manager in a valid volume manager disk group .One or more disks separated by space can be selected for adding into volume manager.

The following disk device has a valid VTOC, but does not appear to have

been initialized for the Volume Manager. If there is data on the disk

that should NOT be destroyed you should encapsulate the existing disk

partitions as volumes instead of adding the disk as a new disk.

Output format: [Device_Name]

c1t2d0

Encapsulate this device? [y,n,q,?] (default: y) n

c1t2d0

Instead of encapsulating, initialize? [y,n,q,?] (default: n) y

Initializing device c1t2d0.

Adding disk device c1t2d0 to disk group rootdg with disk

name disk39.

Add or initialize other disks? [y,n,q,?] (default: n)

2.2 Encapsulate one or more disks

This is used to bring the disk under volume manager , which are already present in the system with data but without volume manager . Data on these disks are not disturbed and if these disks meets certain volume manager requirements these are added under volume manager.

System needs rebooting if encapsulation is used for disk with mounted filesystem or running applications . Also the old device names needs to be changed in applications/scripts to reflect the new volume name.

Use this operation to convert one or more disks to use the Volume Manager.

This adds the disks to a disk group and replaces existing

partitions

with volumes. Disk encapsulation requires a reboot for the

changes to take effect.

Which disk group [,list,q,?] (default: rootdg)

Use a default disk name for the disk? [y,n,q,?] (default: y)

The selected disks will be encapsulated and added to the rootdg

disk group with default disk names.

The disk device c2t5d0 will be encapsulated and added to the disk

group rootdg with the disk name disk01.

The c2t5d0 disk has been configured for encapsulation.

The first stage of encapsulation has completed successfully. You

should now reboot your system at the earliest possible opportunity.

The encapsulation will require two or three reboots which will happen automatically after the next reboot. To reboot execute the command:

shutdown -g0 -y -i6

This will update the /etc/vfstab file so that volume devices are

used to mount the file systems on this disk device. You will need to update any other references such as backup scripts, databases,

or manually created swap devices.

The disk device c2t5d0 will be encapsulated and added to the disk group rootdg with the disk name disk01.

The encapsulation operation failed with the following error:

It is not possible to encapsulate c2t5d0, for the following reason:

This option is used to remove a disk from a disk group provided there is no active volume using this disk .. If there are some volumes using the disk the those have to be either moved to some other disk or removed if they are no longer needed.

However since a diskgroup must have at least one disk you can not remove all the disks from a disk group . To remove all disks from a diskgroup you have to disable the volume group with the exception of rootdg disk group which can not be disabled .

Use this operation to remove a disk from a disk group. This

operation takes, as input, a disk name. This is the same name

that you gave to the disk when you added the disk to the disk

group.

This option is used for removing the disk but retaining the name of the disk so that it can be used by the newly replaced disk . The replacement disk can be a newly added disk or already available disk in the other disk groups

Use this menu operation to remove a physical disk from a disk

group, while retaining the disk name. This changes the state

for the disk name to a removed disk. If there are any

initialized disks that are not part of a disk group, you will be

given the option of using one of these disks as a replacement.

This operation can be used to mirror volumes on a disk. These

volumes can be mirrored onto another disk or onto any

available disk space. Volumes will not be mirrored if they are

already mirrored. Also, volumes that are comprised of more than

one subdisk will not be mirrored.

2.7 Move volumes from a disk

This option is used in case the disk is to be replaced or removed and has active volumes on the disk. . Also volumes can be moved to different disk groups for better space , performance etc.

Use this menu operation to move any volumes that are using a

disk onto other disks. Use this menu immediately prior to

removing a disk, either permanently or for replacement. You can

specify a list of disks to move volumes onto, or you can move the

volumes to any available disk space in the same disk group.

NOTE: Simply moving volumes off of a disk, without also removing

the disk, does not prevent volumes from being moved onto

the disk by future operations. For example, using two

consecutive move operations may move volumes from the

second disk to the first.

You can now specify a list of disks to move onto. Specify a list

of disk media names (e.g., disk01) all on one line separated by

blanks. If you do not enter any disk media names, then the

volumes will be moved to any available space in the disk group.

2.8 Enable access to (import) a disk group

Used in enabling ownership of the other system to a disk group which has been deported by the other system. Used in failover configurations where the ownership of a shared disk/disk group is transferred to the other system in case of failure of current system.

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