SvHCI & SvSAN - Software RAID

SvSAN supports both hardware RAID controllers and Host Bus Adapters (HBAs). When using a hardware RAID controller, the VSA sees a JBOD disk, allowing all RAID functionality provided by the controller to be fully supported, including RAID 0, RAID 1, RAID 10, RAID 5/50, and RAID 6/60.

The performance delivered to the VSA depends on the RAID configuration selected. For example, parity RAID provides excellent storage efficiency with HDDs but can deliver poor write performance if the controller does not include a cache module.

Some RAID controllers also disable write caching when SSD Smart Path is enabled. Reference:

SvSAN and HPE SSD Smart Path 

When an HBA is used, the physical drives are passed directly through the hypervisor to the VSA for management.

One advantage of hardware RAID volumes assigned to the VSA through RDM or JBOD is that storage can be expanded easily. After increasing the RAID volume on the controller, the VSA automatically detects the larger capacity.

Reference:

Increasing Storage using the vCenter Plugin 

Software RAID volumes cannot be dynamically expanded. Expanding a software RAID configuration requires breaking the mirror, deleting the storage pool, recreating it, and allowing synchronization to complete.

Reference:

SvSAN Plex Delete / Break 

For this reason, when using a hardware RAID controller, a JBOD pool is generally recommended instead of RAID0.

SvSAN VSAs leverage the Linux MD (Multiple Device) subsystem internally to provide software RAID functionality. Supported software RAID levels include:

• RAID 0 (Stripe)
• RAID 1 (Mirror)
• RAID 10

These software RAID types can be used for either cache SSD devices or storage pool disks depending on the deployment requirements.

RAID 5 is not provided by the Linux software RAID implementation used by SvSAN. This is intentional due to the poor write performance associated with parity calculations when no hardware write cache is available, along with the potential for write-hole scenarios.

Hardware RAID adapters remain fully supported for parity RAID implementations such as RAID5, RAID50, RAID6 and RAID60.

Additional information regarding supported HPE Smart Array RAID controllers can be found here:

HPE Smart Array Documentation 

If multiple disks are simply added together as a JBOD inside the VSA, the result becomes a concatenated storage pool. This provides the full usable capacity of all disks but does not increase performance beyond that of a single drive.

The SvSAN vCenter Plugin simplifies deployment by allowing storage to be assigned to the VSA during the deployment wizard.

During deployment, storage can initially be assigned as one of the following:

• Single RDM
• Single VMDK
• Skip storage assignment

Selecting Advanced Options exposes additional storage configuration choices, allowing multiple disks to be assigned directly during deployment.

Multiple disks may be configured as either:

• JBOD
• Software RAID1

A common deployment method is to assign the disks initially as JBOD to speed deployment. Once the VSA is online, the temporary JBOD pool can be removed and replaced with a software RAID10 configuration using the VSA WebGUI.

The SvSAN VSA WebGUI provides access to all supported software RAID functionality, including RAID0, RAID1, RAID10 and Hot Spare configuration.

Unlike the deployment plugin, the WebGUI supports creating software RAID10 pools after deployment has completed.

Hot Spare disks may also be assigned through the WebGUI by selecting the desired storage pool and choosing Add Hot Spare.

Select the disk that will act as the dedicated Hot Spare for the software RAID volume.

Once assigned, the Hot Spare is displayed within the storage pool and will automatically participate if a protected disk fails.

• StorMagic Product Documentation 
• SvSAN and HPE SSD Smart Path 
• SvSAN Plex Delete / Break 
• Increasing Storage Using the vCenter Plugin