SANtricity 11 Manuals (CA08872-010)
Decide whether to use a pool or a volume group
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
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If you need faster drive rebuilds and simplified storage administration, require thin volumes, and/or have a highly random workload.
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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
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If you need maximum system bandwidth, the ability to tune storage settings, and a highly sequential workload.
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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.
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If you want to write the data for each volume sequentially across the set of drives that comprise the volume group.
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Because pools can co-exist with volume groups, a storage system 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 (Only from SMcli) |
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 system 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 SANtricity System Manager. |
Yes. RAID 0, 1, 10, 5, and 6 available. |
Thin volumes supported |
Yes (Only from SMcli) |
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 system |
RAID 1 and 10—up to the maximum limit of the storage system 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 system 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 |
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Mixed drive types (HDD, SSD) are not supported for either pools or volume groups. |
