VxVM:
VxVM is a storage management
subsystem that allows to manage physical disks as logical devices called
volumes.
Provides easy-to-use online disk
storage management for computing environments and SAN environments.
VxVM volumes can span multiple
disks.
Provides tools to improve
performance and ensure data availability and integrity.
VxVM and the Operating System:
Operates as a subsystem between OS
and data management systems
VxVM depends on OS for the following:
OS
disk devices
Device
handles
VxVM
dynamic multipathing (DMP) Metadevice
VxVM relies on the following
daemons:
vxconfigd: Configuration daemon
maintains disk and group configurations and communicates configuration changes
to the kernel.
vxiod: VxVM I/O daemon provides
extended I/O operations.
vxrelocd: The hot-relocation daemon
monitors VxVM for events that affect redundancy, and performs hot-relocation to
restore redundancy.
VxVM Storage Management:
VxVM uses two types of objects to
handle storage management.
Physical objects:
Basic storage device where the data
is ultimately stored
Device names – c#t#d#s#
Virtual objects:
When one or more physical disks are
brought under the control of VxVM, it creates virtual objects called “volumes”.
Virtual Objects in VxVM:
VM Disks
Disk Groups
Sub disks
Plexes
Volumes
VM Disks:
When a physical disk is placed
under VxVM control, a VM disk is assigned to the physical disk.
VM disk typically includes a public
region (allocated storage) and a private region where internal configuration
information is stored.
VM disk has a unique name (disk
media name, can be maximum 31 characters, by default takes disk## format).
Disk Groups:
Is a collection of VM disks that
share a common configuration.
The default disk group is “rootdg”.
Disk group name can e max 31
characters.
Allows to group disks into logical
collections.
Volumes are created within a disk
group.
Subdisks:
Is a set of contiguous disk blocks.
A VM disk can be divided into one
or more subdisks.
Default name for VM disk is disk##
(disk01) and default name for subdisk is disk##-## (disk01-01).
Any VM disk space that is not part
of a subdisk is free space and can be used for creating new subdisks.
Plexes:
VxVM uses subdisks to build virtual
objects called plexes.
A plex consists of one or more
subdisks located on one or more physical disks.
Volumes:
Is a virtual disk device that
appears to applications.
Consists of one or more plexes.
Default naming convention for a
volume is vol## and default naming convention for plexes in a volume is
vol##-##.
Volume can contain upto 31
characters.
Can consist of up to 32 plexes.
Must have at least one plex
associated.
All subdisk within a volume must
belong to the same disk group.
Combining Virtual objects in
VxVM:
VM disks are grouped in to sub disk
groups.
Volume Layouts in VxVM:
Non-layered Volumes:
Sub disk is restricted to mapping
directly to a VM disk.
Layered Volumes:
Is constructed by mapping its
subdisks to underlying volumes.
Layout Methods:
Concatenation and Spanning
Striping (RAID 0)
Mirroring (RAID 1)
Striping + Mirroring (Mirrored
Stripe or RAID 0+1)
Mirroring + Striping (Striped
Mirror or RAID 1+0)
RAID 5 (striping with Parity)
Online Relayout:
Online relayout allows to change
the storage layouts that have been created already without disturbing data
access.
Dirty Region Logging (DRL):
DRL is enabled, speeds recovery of
mirrored volumes after a system crash.
DRL keeps track of the regions that
have changed due to I/O writes to a mirrored volume.
DRL uses this information to
recover only those portions of the volumes that needed to be recovered.
Fast Resync:
Performs quick and efficient
resynchronization of stale mirrors (a mirror that is not synchronized).
Hot-Relocation:
Feature that allows a system to
react automatically to I/O failures on redundant objects in VxVM and restore
redundancy and access to those objects.
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