IBM V7000 Volume types explained SAN Admins should know

A volume is a logical disk that the system presents to attach hosts. In this article we are going to learn IBM v7000 Volume types explained SAN admins should Know.

Application servers access volumes, not MDisks or drives. To keep a volume accessible even when an MDisk on which it depends has become unavailable, a mirrored copy can be added to a selected volume. Each volume can have a maximum of two copies. Each volume copy is created from a set of extents in a pool.

IBM V7000 Volume types explained SAN Admins should know

You can create different types of volumes, depending on the type of topology that is configured on your system. For example, in standard topology, which is single-site configuration, you can create basic, mirrored, or custom volumes. If you have a HyperSwap topology, which is two-site configuration, you can create basic, HyperSwap, or custom volumes. For each of these volume types you can specify specific details, such as a method of capacity savings for the volumes.

The system supports compression and thin provisioning to save space on volumes. With compressed volumes, data is compressed as it is written to the volume, which saves capacity on the volume. Thin provisioning creates a volume with more virtual than real capacity that allows the capacity to grow as it is needed.

The system uses base-2 (binary numeral) as capacity indicators for volumes, drives, and other system objects. The management GUI and the command-line interface (CLI) use different abbreviations to indicate capacity, but the value for these capacity indicators is the same. IBM V7000 Volume types

The following table displays the differences in how capacity indicators are displayed in the management GUI and the CLI. IBM V7000 Volume types

Table 1. Capacity indicators. This table displays the differences in how capacity indicators are displayed in the management GUI and the CLI.
Metric	GUI Abbreviation	CLI Abbreviation	Value
kibibyte	KiB	KB	1024
mebibyte	MiB	MB	1,048,576
gibibyte	GiB	GB	1,073,741,824
tebibyte	TiB	TB	1,099,511,627,776
pebibyte	PiB	PB	1,125,899,906,842,624
exbibyte	EiB	EB	1,152,921,504,606,846,976
zebibyte	ZiB	ZB	1,180,591,620,717,411,303,424
yobibyte	YiB	YB	1,208,925,819,614,629,174,706,176

Basic volumes

A basic volume is the simplest type of volume, consisting of a copy in a single storage pool.

Mirrored volume

By using volume mirroring, a volume can have two physical copies. Each volume copy can belong to a different pool, and each copy has the same virtual capacity as the volume. In the management GUI, an asterisk (*) indicates the primary copy of the mirrored volume. The primary copy indicates the preferred volume for read requests

HyperSwap volumes
HyperSwap volumes create copies on separate sites for systems that are configured with HyperSwap topology. Data that is written to a HyperSwap volume is automatically sent to both copies so that either site can provide access to the volume if the other site becomes unavailable.

Custom volumes
Custom volumes create volumes that are based on user-defined customization rather than taking the standard default settings for each of the options under quick volume creation.

Thin-provisioned volumes

When you create a volume, you can designate that it is thin-provisioned to save capacity for the volume. A thin-provisioned volume has different virtual capacity and a real capacity.

Compressed volumes
When you create volumes, you can specify compression as a method to save capacity for the volume. With compressed volumes, data is compressed as it is written to disk, saving additional space. To use the compression function, you must obtain the IBM Real-time Compression license.

Change volumes
Change volumes are used in Global Mirror relationships and between HyperSwap volume copies. Change volumes create periodic point-in-time-copies of the source volumes and replicate them to the secondary site. Using change volumes lowers bandwidth requirements by only addressing the average throughput and not the peak.

Move volumes to another I/O group
You can move a volume to a new I/O group to balance the workload across the canisters in the system without stopping host activity to the volumes. The wizard changes only the I/O group for the volume and does not change where the data resides on the backend storage. SAN admins

Moving volumes mapped to iSCSI hosts to another I/O group
To move volumes that are mapped to iSCSI hosts to another I/O group, you must unmap the volumes from the hosts before you run the Move Volume to Another I/O Group wizard. SAN admins

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