1.Advantages of Disksuite

2. Disksuite terms

3. Disksuite Packages

4. Installing
DiskSuite 4.2.1 in Solaris 8

5. Creating State
Database

6. Creating MetaDevices

6.1. Concatenated
Metadevice

6.2. Striped
Metadevice

6.3 Mirrored Metadevice

6.3.1 Simple mirror

6.3.2 Mirroring a unmountable Partition

6.3.3 root mirroring & /usr mirroring

6.3.4  Making alternate  root disk bootable

6.3.5 Setting
alternate boot path for root mirror

6.4 RAID 5

6.5 TransMeta Device

6.5.1 TransMeta device for unmountable partition

6.5.2 TransMeta device for non unmountable partition.

6.5.3 TransMeta
device using Mirror

6.6 Hotspare Pool

6.6.1 Adding a Hotspare to Mirror

6.6.2 Adding a Hotspare to RAID5

6.6.3 Adding a disk to Hotspare Pool.

6.7 disksets

6.7.1 Creating two diskset

6.7.2 Adding disk to diskset

6.7.3 Creating Mirror in Diskset

7.  TroubleShooting

7.1) Recovering from  Stale State Database replicas

7.2) Metadevice Errors

1. Advantages of Disksuite

Solstice disk suite provides three major functionalities :

1. Over come the disk size limitation by providing for joining of
multiple disk slices to form a bigger  volume. 

2. Fault Tolerance by allowing mirroring of data from one disk to another
and keeping parity 
    information in RAID5. 

3. Performance enhancement by allowing spreading the data space over
multiple disks .

2. Disksuite terms

Metadevice :A virtual device composed of several physical devices -
slices/disks  . All the operations are carried out using metadevice
name and transparently implemented on the individual device.

RAID : A group of disks used for creating a virtual volume is called array and
depending on disk/slice arrangement these are called various types of RAID
(Redundant Array of Independent Disk ).

RAID 0 Concatenation/Striping

RAID 1 Mirroring

RAID 5 Striped array with rotating parity.

Concatenation :Concatenation is joining of two or more disk slices to add up the disk space
. Concatenation is serial in nature i.e. sequential data operation are performed
serially on first disk then second disk and so on . Due to serial nature new
slices can be added up without having to take the backup of entire concatenated
volume ,adding slice and restoring backup .

Striping :Spreading of data over multiple disk drives mainly to enhance the performance
by distributing data in alternating chunks – 16 k interleave across the stripes
. Sequential data operations are performed in parallel on all the stripes by
reading/writing  16k data blocks alternatively form the disk stripes.

Mirroring : Mirroring provides data redundancy by simultaneously writing data on to two
sub mirrors of a mirrored device . A submirror can be a stripe or concatenated
volume and a mirror can have three mirrors . Main concern here is that a mirror
needs as much as the volume to be mirrored.

RAID 5 : RAID 5 provides data redundancy and advantage of striping and uses less space
than mirroring . A RAID 5 is made up of at least three disk which are striped
with parity information written alternately on all the disks . In case of a
single disk failure the data can be rebuild using the parity information from
the remaining disks .

3. Disksuite Packages :

Solstice disk suite is a part of server edition of the Solaris OS and is not
included with desktop edition . The software is in pkgadd format & can be
found in following locations in CD :

Solaris 2.6 – “Solaris Server Intranet Extensions 1.0” CD.

Solaris 7 – “Solaris Easy Access Server 3.0”

Solaris 8 – “Solaris 8 Software 2 of 2”

Solaris 2.6 & 2.7 Solstice Disk suite version is 4.2 .  Following packages are part of it but only the "SUNWmd" is the
minimum required package and a patch.

SUNWmd – Solstice DiskSuite

SUNWmdg – Solstice DiskSuite Tool

SUNWmdn – Solstice DiskSuite Log Daemon

Patch No. 106627-04 (obtain latest revision)

Solaris 8 DiskSuite version is 4.2.1 .Following are the minimum required packages ..

SUNWmdr Solstice DiskSuite Drivers (root)

SUNWmdu Solstice DiskSuite Commands

SUNWmdx Solstice DiskSuite Drivers (64-bit)

4. Installing DiskSuite 4.2.1 in Solaris 8

# cd /cdrom/sol_8_401_sparc_2/Solaris_8/EA/products/DiskSuite_4.2.1/sparc/Packages

# pkgadd -d .

The following packages are available:

1 SUNWmdg Solstice DiskSuite Tool

(sparc) 4.2.1,REV=1999.11.04.18.29

2 SUNWmdja Solstice DiskSuite Japanese
localization

(sparc) 4.2.1,REV=1999.12.09.15.37

3 SUNWmdnr Solstice DiskSuite Log Daemon
Configuration Files

(sparc) 4.2.1,REV=1999.11.04.18.29

4 SUNWmdnu Solstice DiskSuite Log Daemon

(sparc) 4.2.1,REV=1999.11.04.18.29

5 SUNWmdr Solstice DiskSuite Drivers

(sparc) 4.2.1,REV=1999.12.03.10.00

6 SUNWmdu Solstice DiskSuite Commands

(sparc) 4.2.1,REV=1999.11.04.18.29

7 SUNWmdx Solstice DiskSuite Drivers(64-bit)

(sparc) 4.2.1,REV=1999.11.04.18.29

Select 1,3,4,5,6,7 packages .

Enter ‘yes’ for the questions asked during installation and reboot the
system after installation .

Put /usr/opt/SUNWmd/bin in root PATH as the DISKSUITE commands are located in
this directory

5. Creating State Database :

State meta database , metadb , keeps information of the metadevices and is
needed for Disksuite operation . Disksuite can not function without metadb so a
copy of replica databases is placed on different disks to ensure that a copy is
available in case of a complete disk failure .

Metadb needs a dedicated disk slice so create partitions of about 5 Meg. on
the disks for metadb. If there is no space available for metadb then it can be
taken from swap . Having metadb on two disks can create problems as DISKSUITE
looks for database replica number > 50% of total replicas and if one of the
two disks crashes the replica falls at 50% . On next reboot system will go to
single user mode and one has to recreate additional replicas to correct the
metadb errors.

The following command creates three replicas of metadb on three disk slices.

Metadevices can be created in two ways

1. Directly from the command line

2. Editing the /etc/opt/SUNWmd/<md.tab.html>
file as per example given in the md.tab and

    initializing devices on command
line using metainit <device name> .

6.1 ) Creating a concatenated Metadevice :

#metainit    d0   
3    1    /dev/dsk/c0t0d0s4 1 /dev/dsk/c0t0d0s4
1 /dev/dsk/c0t0d0s4

d0 – metadevice name

3 – Total Number of Slices

1 – Number of Slices to be added followed by slice name.

6.2 ) Creating a stripe
of 32k interleave

# metainit d10     1     2     c0t1d0s2     c0t2d0s2     -i   32k

d0 – metadevice name

1 – Total Number of Stripe

2- Number of Slices to be added to stripe followed by slice name .

-i chunks of data written alternatively on stripes.

A mirror is a metadevice composed of one or more submirrors. A
submirror is made of one or more striped or concatenated metadevices. Mirroring
data provides you with maximum data availability by maintaining multiple copies
of your data. The system must contain at least three state database replicas
before you can create mirrors. Any file system including root (/),
swap, and /usr,
or any application such as a database, can use a mirror.

1.Create two stripes for two submirors as d21 & d22

#
metainit d21 1 1 c0t0d0s2

d21: Concat/Stripe is setup

#
metainit t
d22 1 1 c1t0d0s2

d22: Concat/Stripe is setup

2. Create a mirror device (d20) using one of the submirror (d21)

#
metainit   d20   -m   d21

d20: Mirror is setup

3. Attach the second submirror (D21) to the main mirror device (D20)

# metattach d20 d22

d50: Submirror d52 is attached.

4. Make file system on new metadevice

#newfs /dev/md/rdsk/d20

edit /etc/vfstab to mount the /dev/dsk/d20 on a mount point.

6.3.2.) Mirroring a Partitions with data which can be unmounted

# metainit f
d1 1 1 c1t0d0s0

d1: Concat/Stripe is setup

# metainit d2 1
1 c2t0d0s0

d2: Concat/Stripe is setup

# metainit d0 -m
d1

d0: Mirror is setup

# umount /local

(Edit the /etc/vfstab file so that the file system references the mirror)

#mount /local

#metattach d0 d2

d0: Submirror d2 is attached

6.3.3 ) Mirroring a Partitions with data which can not be unmounted – root and /usr

· /usr mirroring

# metainit -f d12 1 1 c0t3d0s6

d12: Concat/Stripe is setup

# metainit d22 1 1 c1t0d0s6

d22: Concat/Stripe is setup

# metainit d2 -m d12

d2: Mirror is setup

(Edit the /etc/vfstab file so that /usr references the mirror)

# reboot

…

…

# metattach d2 d22

d2: Submirror d22 is attached

· root mirroring

# metainit -f d11 1 1 c0t3d0s0

d11: Concat/Stripe is setup

# metainit d12 1 1 c1t3d0s0

d12: Concat/Stripe is setup

# metainit d10 -m d11

d10: Mirror is setup

# metaroot d10

# lockfs -fa

# reboot

…

…

# metattach d10 d12

d10: Submirror d12 is attached

6.3.4  ) Making Mirrored disk bootable

a.) # installboot /usr/platform/`uname -i`/lib/fs/ufs/bootblk
/dev/rdsk/c0t1d0s0

6.3.5  ) Creating alterbate name for Mirrored boot disk

a.) Find physical path name for the second boot disk

# ls -l /dev/rdsk/c1t3d0s0

lrwxrwxrwx 1 root root 55 Sep 12 11:19 /dev/rdsk/c1t3d0s0 ->../../devices/sbus@1,f8000000/esp@1,200000/sd@3,0:a

b.) Create an alias for booting from disk2

ok> nvalias bootdisk2 /sbus@1,f8000000/esp@1,200000/sd@3,0:a

ok> boot bootdisk2

6.4 Creating a RAID 5 volume :

The system must contain at least three state
database replicas before you can create RAID5 metadevices.

A RAID5 metadevice can only handle a single
slice failure.A RAID5 metadevice can be grown by concatenating additional slices
to the metadevice. The new slices do not store parity information, however they
are parity protected. The resulting RAID5 metadevice continues to handle a
single slice failure. Create a RAID5 metadevice from a slice that
contains an existing file system.will erase the data during the RAID5
initialization process .The interlace value is key to RAID5 performance. It is
configurable at the time the metadevice is created; thereafter, the value cannot
be modified. The default interlace value is 16 Kbytes which is reasonable for
most of the applications.

6.4.1.) To setup raid5 on three slices of different disks .

# metainit d45 -r c2t3d0s2 c3t0d0s2 c4t0d0s2

d45: RAID is setup

6.5.)
Creating a Trans Meta Device :

Trans meta devices enables ufs logging . There is one logging device and a
master device and all file system changes are written into logging device and
posted on to master device . This greatly reduces the fsck time for very large
file systems as fsck has to check only the logging device which is usually of 64
M. maximum size.Logging device preferably should be mirrored and located on a different drive
and controller than the master device .

Ufs logging can not be done for root partition.

6.5.1) Trans Metadevice for a File System That Can Be Unmounted

· /home2

1. Setup metadevice

# umount /home2

# metainit d63 -t c0t2d0s2 c2t2d0s1

d63: Trans is setup

Logging becomes effective for the file system when it is remounted

2. Change vfstab entry & reboot

from

/dev/md/dsk/d2 /dev/md/rdsk/d2 /home2 ufs 2 yes -

to

/dev/md/dsk/d63 /dev/md/rdsk/d63 /home2 ufs 2 yes -

# mount /home2

Next reboot displays the following message for logging device

# reboot

…

/dev/md/rdsk/d63: is logging

6.5.2
) Trans Metadevice for a File System That Cannot Be Unmounted

· /usr

1.) Setup metadevice

# metainit -f d20 -t c0t3d0s6 c1t2d0s1

d20: Trans is setup

2.) Change vfstab entry & reboot:

from

/dev/dsk/c0t3d0s6     /dev/rdsk/c0t3d0s6   /usr   ufs      1     no     -

to

       /dev/md/dsk/d20      /dev/md/rdsk/d20     /usr    ufs     1     no     -

        # reboot

1.) Setup metadevice

#umount /home2

#metainit     d64     -t     d30     d12

d64 trans is setup

2.) Change vfstab entry & reboot:

from

/dev/md/dsk/d30 /dev/md/rdsk/d30 /home2 ufs 2 yes

to

/dev/md/dsk/d64 /dev/md/rdsk/d64 /home2 ufs 2 yes

6.6 ) HotSpare Pool

A hot spare pool is a collection of slices reserved by DiskSuite to be
automatically substituted in case of a slice failure in either a submirror or
RAID5 metadevice . A hot spare cannot be a metadevice and it can be associated
with multiple submirrors or RAID5 metadevices. However, a submirror or RAID5
metadevice can only be asociated with one hot spare pool. .Replacement is based on a first fit for the failed slice and they need to be
replaced with repaired or new slices. Hot spare pools may be allocated,
deallocated, or reassigned at any time unless a slice in the hot spare pool is
being used to replace damaged slice of its associated metadevice.

6.6.1) Associating a Hot Spare Pool with Submirrors

# metaparam -h     hsp100    
d10

# metaparam -h     hsp100    
d11

# metastat d0

d0: Mirror

Submirror 0: d10

State: Okay

Submirror 1: d11

State: Okay

…

d10: Submirror of d0

State: Okay

Hot spare pool: hsp100

…

d11: Submirror of d0

State: Okay

Hot spare pool: hsp100

#metaparam     -h   
hsp001     d10

#metastat     d10

d10:RAID

State: Okay

Hot spare Pool: hsp001

6.6.3 ) Adding a Hot Spare Slice to All Hot Spare Pools

# metahs   -a    -all   
/dev/dsk/c3t0d0s2

hsp001: Hotspare is added

hsp002: Hotspare is added

hsp003: Hotspare is added

 

Few important points about disksets :

• A diskset is a set of shared disk drives containing
  DiskSuite objects that can be shared exclusively (but not concurrently)
  by one or two hosts. Disksets are used in high availability failover
  situations where the ownership of the failed machine’s diskset is
  transferred to other machine . Disksets are connected to two hosts for
  sharing and must have  same attributes , controller/target/drive ,
  in both machines except for the ownership .

• DiskSuite must be installed on each host that will be connected to the
  diskset.There is one metadevice state database per shared diskset and one on
  the "local" diskset. Each host must have its local metadevice
  state database set up before you can create disksets.

  Each host in a diskset must have a local diskset besides a shared diskset.A diskset can be created seprately on one host  &  then
  added to  the second host later.

• Drive should not be in use by a  file system, database, or any other
  application for adding in diskset .

6.7.1 ) Creating Two Disksets

host1# metaset   -s    diskset0  
-a   -h    host1    host2

host1# metaset   -s   
diskset1  -a    -h    host1   
host2

host1# metaset

Set name = diskset0, Set number = 1

Host           Owner

host1

host2

Set name = diskset1, Set number = 2

Host          Owner

host1

host2

6.7.2 ) Adding Drives to a Diskset

host1# metaset     -s      
diskset0     -a    c1t2d0  c1t3d0  c2t2d0  
c2t3d0   c2t4d0   c2t5d0

 

host1# metaset

Set name = diskset0, Set number = 1

Host        Owner

host1       Yes

host2

 

Drive            Dbase

c1t2d0         Yes

c1t3d0         Yes

c2t2d0         Yes

c2t3d0         Yes

c2t4d0         Yes

c2t5d0         Yes

 

Set name = diskset1, Set number = 2

Host          Owner

host1

host2

6.7.3 ) Creating  a Mirror in a Diskset 

# metainit -s diskset0 d51   1  
1   /dev/dsk/c0t0d0s2

diskset0/d51: Concat/Stripe is setup

 

# metainit -s diskset0 d52   1  
1   /dev/dsk/c1t0d0s2

diskset0/d52: Concat/Stripe is setup

 

# metainit -s diskset0 d50   -m  
d51

diskset0/d50: mirror is setup

 

# metattach -s diskset0   d50    
d52

diskset0/d50: Submirror d52 is attached

7.0 Trouble Shooting

7.1 ) Recovering from  Stale State Database Replicas

Problem    : State database
corrupted or unavailable .

Causes      : Disk failure , Disk I/O
error.

Symptoms : Error message at the booting time if databases are <=
50% of total database. System comes to Single user mode.

ok boot
…
Hostname: host1
metainit: Host1: stale databases
Insufficient metadevice database replicas located.
Use metadb to delete databases which are broken.
Ignore any "Read-only file system" error messages.
Reboot the system when finished to reload the metadevice
database.
After reboot, repair any broken database replicas which were
deleted.
Type Ctrl-d to proceed with normal startup,
(or give root password for system maintenance): <root-password>
Entering System Maintenance Mode.

1.) Use the metadb command to look at the metadevice state database
and see which state database replicas are not available. Marked by unknown and M
flag.

# /usr/opt/SUNWmd/metadb -i
   flags      first blk     
block count
    a m  p  lu    16                 
1034                
/dev/dsk/c0t3d0s3
    a      p  l     
1050             
1034               
/dev/dsk/c0t3d0s3
    M    p       
unknown      unknown             
/dev/dsk/c1t2d0s3
    M    p       
unknown      unknown                     

2.) Delete the state database replicas on the bad disk using the -d
option to the metadb(1M) command.

At this point, the root (/) file system
is read-only. You can ignore the mddb.cf error messages:

 

# /usr/opt/SUNWmd/metadb  -d  -f 
c1t2d0s3
metadb: demo: /etc/opt/SUNWmd/mddb.cf.new: Read-only file system .

 

Verify deletion

# /usr/opt/SUNWmd/metadb  -i
    flags        first blk      
block count
     a m  p  lu        
16             
1034            /dev/dsk/c0t3d0s3
     a      p  l         
1050           1034          
/dev/dsk/c0t3d0s3

3.) Reboot.

4.) Use the metadb command to add back the state database replicas
and to see  that the state database replicas are correct.

# /usr/opt/SUNWmd/metadb -a -c 2 c1t2d0s3

# /usr/opt/SUNWmd/metadb

   flags        first blk 
block count
  a m  p  luo     
16          
1034         dev/dsk/c0t3d0s3
  a    p  luo     
1050        
1034         dev/dsk/c0t3d0s3
  a      
u       
16          
1034         dev/dsk/c1t2d0s3
  a      
u       
1050        
1034         dev/dsk/c1t2d0s3

7.2 ) Metadevice Errors :

Problem    : Sub Mirrors out of sync  in 
"Needs maintainence" state ,

Causes      : Disk problem / failure ,
improper shutdown , communication problems between two mirrored disks .

symptoms : "Needs maintainence" errors in metastat output

# /usr/opt/SUNWmd/metastat d0: Mirror     Submirror 0: d10       State: Needs maintenance     Submirror 1: d20       State: Okay … d10: Submirror of d0     State: Needs maintenance     Invoke: "metareplace d0 /dev/dsk/c0t3d0s0 <new device>"     Size: 47628 blocks     Stripe 0: Device              Start Block  Dbase State        Hot Spare /dev/dsk/c0t3d0s0          0     No    Maintenance   d20: Submirror of d0     State: Okay     Size: 47628 blocks     Stripe 0: Device              Start Block  Dbase State        Hot Spare /dev/dsk/c0t2d0s0          0     No    Okay

Solution :

1.)    If disk is all right  -  enable the 
failed metadevice  with metareplace command  .

        If disk is failed – Replace
disk create similar partitions as in failed disk and enable new device with
metareplace command.

        # /usr/opt/SUNWmd/metareplace -e d0 c0t3d0s0
       
Device /dev/dsk/c0t3d0s0 is enabled
 
2.)  If disk has failed  and you want to move the failed devices to
new disk with different id (CnTnDn) – add new disk ,

       format to create    
a similar partition scheme as in failed disk and use metarepalce command

       # /usr/opt/SUNWmd/metareplace  d0 c0t3d0s0  
<new device name>

The metareplace command above can also be used for concate or strip 
replacement in a  volme but that would involve restoring the backup if it
is not mirrored.

About Vxassist
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
12.Next Steps

About vxassist

vxassist command syntax :

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

Device Nodes
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

NextPage Creating a Volume

Veritas Volume Manager is used to manage disk storage spread over an array of disks.

The main 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 .

The following article describes the volume manager objects and configuration of these objects using a text menu based utility called vxdiskadm .

Table of Contents :
1. Volume Manager Objects
1.1 Disks
1.2 Disk groups
1.3 Volume Manager disks
1.4 Subdisks
1.5 Plexes
1.6 Volumes
1.7 Volume Manger Objects & their Relationship

2. Volume Manager Configuration ( options menu)
2.1 Add or initialize one or more disks
2.2 Encapsulate one or more disks
2.3 Remove a disk
2.4 Remove a disk for replacement
2.5 Replace a failed or removed disk
2.6 Mirror volumes on a disk
2.7 Move volumes from a disk
2.8 Enable access to (import) a disk group
2.9 Remove access to (deport) a disk group
2.10 Enable (online) a disk device
2.11 Disable (offline) a disk device
2.12 Mark a disk as a spare for a disk group
2.13 Turn off the spare flag on a disk

1.0 Volume Manager Objects
Disks
Disks are referred in volume manager by two terms – device name and disk name . The device name specifies controller , target id and slice of the disk . Disk name is the common name given to the device name as an easy to remember name .

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.

Subdisks
* A subdisk is a subsection of a disk’s public region and is the smallest unit of storage in Volume Manager.
* A subdisk is defined by an offset and a length in sectors on a volume manager disk.
* A volume manager disk can contain multiple subdisks but subdisks cannot overlap or share the same portions of a volume manager disk.
* volume manager disk space that is not reserved or that is not part of a subdisk is free space. You can use free space to create new subdisks.

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.

Plexes

* A plex is a structured or ordered collection of subdisks that represents one copy of the data in a volume. A plex consists of one or more subdisks located on one or more physical disks.
* A plex is also called a mirror. The terms plex and mirror can be used interchangeably, even though a plex is only one copy of the data. The terms “mirrored” or “mirroring” imply two or more copies of data.
* The length of a plex is determined by the last block that can be read or written on the last subdisk in the plex.
* The default naming convention for plexes in a volume is volumename-##. The default plex name consists of the volume name, a hyphen, and a two-digit number

Volumes

* A volume is composed of one or more plexes not restricted by the physical size of the disk.
* A volume can span across multiple disks.
* Volume Manager uses the default naming convention vol## for volumes, where ## represents a two-digit number but can be user defined as per requirement.

Volume Manager Objects and Their Relationship

2.0 Volume Manager Configuration

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 .

Most of the volume manager operation related to disks & volume can be performed by a character based menu utility call vxdiskadm

Following pages describes the use of vxddiskadm to configure and manage volume manager.