Decide whether to use a pool or a volume group

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You can create volumes using either a pool or a volume group. The best selection depends primarily on the key storage requirements such as the expected I/O workload, the performance requirements, and the data protection requirements.

Reasons to choose a pool or volume group

Choose a pool

  • If you need faster drive rebuilds and simplified storage administration, require thin volumes, and/or have a highly random workload.

  • If you want to distribute the data for each volume randomly across a set of drives that comprise the pool.

    You cannot set or change the RAID level of pools or the volumes in the pools. Pools use RAID level 6.

Choose a volume group

  • If you need maximum system bandwidth, the ability to tune storage settings, and a highly sequential workload.

  • If you want to distribute the data across the drives based on a RAID level. You can specify the RAID level when you create the volume group.

  • If you want to write the data for each volume sequentially across the set of drives that comprise the volume group.

Note

Because pools can co-exist with volume groups, a storage array can contain both pools and volume groups.

Feature differences between pools and volume groups

The following table provides a feature comparison between volume groups and pools.

Use Pool Volume group

Workload random

Better

Good

Workload sequential

Good

Better

Drive rebuild time

Faster

Slower

Performance (optimal mode)

Good: Best for small block, random workload.

Good: Best for large block, sequential workloads

Performance (drive rebuild mode)

Better: Usually better than RAID 6

Degraded: Up to 40% drop in performance

Multiple drive failures

Greater data protection: Faster, prioritized rebuilds

Less data protection: Slow rebuilds, greater risk of data loss

Adding drives

Faster: Add to pool on the fly

Slower: Requires Dynamic Capacity Expansion operation

Thin volumes support

Yes

No

Solid State Disk (SSD) support

Yes

Yes

Simplified administration

Yes: No hot spares or RAID settings to configure

No: Must allocate hot spares, configure RAID

Tunable performance

No

Yes

Functional comparison of pools and volume groups

The function and purpose of a pool and a volume group are the same. Both objects are a set of drives logically grouped together in a storage array and are used to create volumes that a host can access.

The following table helps you decide whether a pool or volume group best suits your storage needs.

Function Pool Volume Group

Different RAID level supported

No. Always RAID 6 in System Manager.

Yes. RAID 0, 1, 10, 5, and 6 available.

Thin volumes supported

Yes

No

Full disk encryption (FDE) supported

Yes

Yes

Data Assurance (DA) supported

Yes

Yes

Shelf loss protection supported

Yes

Yes

Drawer loss protection supported

Yes

Yes

Mixed drive speeds supported

Recommended to be the same, but not required. Slowest drive determines speed for all drives.

Recommended to be the same, but not required. Slowest drive determines speed for all drives.

Mixed drive capacity supported

Recommended to be the same, but not required. Smallest drive determines capacity for all drives.

Recommended to be the same, but not required. Smallest drive determines capacity for all drives.

Minimum number of drives

11

Depends on RAID level. RAID 0 needs 1. RAID 1 or 10 needs 2 (requires an even number). RAID 5 minimum is 3. RAID 6 minimum is 5.

Maximum number of drives

Up to the maximum limit for the storage array

RAID 1 and 10—​up to the maximum limit of the storage array RAID 5, 6—​30 drives

Can choose individual drives when creating a volume

No

Yes

Can specify segment size when creating a volume

Yes. 128K supported.

Yes

Can specify I/O characteristics when creating a volume

No

Yes. File system, database, multimedia, and custom supported.

Drive failure protection

Uses preservation capacity on each drive in the pool making reconstruction faster.

Uses a hot spare drive. Reconstruction is limited by the IOPs of the drive.

Warning when reaching capacity limit

Yes. Can set an alert when used capacity reaches a percentage of the maximum capacity.

No

Migration to a different storage array supported

No. Requires that you migrate to a volume group first.

Yes

Dynamic Segment Size (DSS)

No

Yes

Can change RAID level

No

Yes

Volume expansion (increase capacity)

Yes

Yes

Capacity expansion (add capacity)

Yes

Yes

Capacity reduction

Yes

No

Note

Mixed drive types (HDD, SSD) are not supported for either pools or volume groups.