 |
The most common Volume Manager for kernel 2.4 is the Logical Volume
Manager (LVM) or LVM2 for kernel 2.6. For kernel 2.6 you can use the
Enterprise Volume Management System (EVMS) as an alternative.
Use LVM and EVMS with striping. The scaling capacities with
Volume Management depend on the connection type:
- ESCON: the number of stripes should be at least equal to the
number of available ESCON channels
- FICON and FCP: the number of stripes should be equal to the
number of disks
- Good stripe sizes are 32KB and 64KB
If the storage server is an IBM TotalStorage
Storage Server then distribute the disks for logical
volumes over several raid arrays and clusters to get best performance. Don't
organize them in only one raid array!
|
Both the Logical Volume Manager2 (LVM2) and the Enterprise
Volume Management System (EVMS) are volume management tools
using the device-mapper for configuring volumes. They differ
in the provided interface, the commands and the terminology
to set up a logical volume. But they offer the same functions.
EVMS provides three interfaces, a graphical interface, a ncurses
based interface and a command line interface. See Volume
management with EVMS to learn how to create a logical
volume with the command line interface. With this interface
it is possible to automatically create a logical volume using
scripts.
Prerequisite: Ensure that the system service "boot.evms"
is turned on to be able to use EVMS as the volume manager. To
turn it on, use the command 'chkconfig -s boot.evms on'.
EVMS provides an online help function to get information about
the commands. The different terminology is listed and compared
below.
|
The device-mapper is a new component supporting logical
volume managers. It is required by LVM2 and EVMS. LVM,
the predecessor of LVM2, does not use it.
For more information see http://sources.redhat.com/dm/.
|
|
The table below gives an overview on the different terms
used within LVM2 and EVMS.
|
Logical Volume
Manager
(LVM and LVM2)
|
Enterprise
Volume Management System (EVMS)
|
EVMS parameters
|
Partition
|
Physical Volume (PV)
|
Segment
|
Size
|
Collection of partitions
|
Volume Groups (VG)
|
Container
|
Physical Extent
Size, default=16MB
|
EVMS specific
|
|
Region
|
Region name,
size in MB or # of extents, striping and stripe_size
|
Logical disk
|
Logical Volume (LV)
|
EVMS volume
|
|
|
|
Disks can be subdivided into smaller storage objects
also called segments. This is done with a Segment Manager;
for the zSeries environment the S/390 Segment Manager
is available. A container allows to combine segments
to get the basis for an EVMS volume. Regions are created
from containers. By creating regions it is possible
to apply special logical volume characteristics like
striping.
Be aware that a region contains at least one extent and
at most 65534 extents and the number must be an integer.
By default all available extents are used. The number
of stripes defines over how many disks the region will
be striped. Striping is not turned on by default. If the
the region will be striped over more than one disk, the
stripe_size must be set. The default stripe_size is 16KB.
EVMS deals differently with EVMS volumes and storage
objects (regions, containers and segments). To be able
to add a file system or mount the volume to the target
system it is necessary to create a volume from a region.
|
|
|
|
|
|
