This is the second in a series of blog posts that will delve into hardware considerations that can be made when building a roll-your-own Virtual SAN environment. The first post of this series covered solid state drive considerations. In this next installment, we will review storage controllers.
Virtual SAN Storage Controller Support
Virtual SAN supports storage controllers in two modes, either pass-through or RAID0 mode. One of the big considerations when choosing a storage controller for Virtual SAN is whether it supports pass-through mode, RAID0 mode, or both.
Storage Controller Pass-Through mode
Certain storage controller HBAs and RAID adapters can support a mode of operation commonly known as pass-through mode, where the vSphere hypervisor is given direct access to the underlying drives. For storage controller HBAs, this is also known as Initiator Target mode (IT Mode), and for RAID controllers that support pass-through, this is known as JBOD mode. Regardless of the nomenclature, the end result gives Virtual SAN complete control of the local SSDs and HDDs attached to the storage controller.
Storage Controller RAID0 mode
For storage controller RAID adapters that do not support pass-through mode, Virtual SAN fully supports RAID0 mode. RAID0 mode is utilized by creating a single drive RAID0 set via the storage controller software, and then presenting this to Virtual SAN. You will then have to mark which of these single drive RAID0 sets are SSDs within vSphere. When RAID0 mode is utilized, the the following occurs
- Virtual SAN will not manage hot-plug capabilities of drives
- Hot-plug will be managed by the storage controller software
To Pass-Through or not to Pass-Through…..
Performance between pass-through and RAID0 mode for the same storage controller should be similar in most instances. When utilizing RAID0 mode, the storage controller cache should be disabled (this is configurable on some, but not all storage controllers) to ensure the storage controller cache does not conflict with the cache of the SSD drives which is controlled by Virtual SAN. When the storage controller cache cannot be completely disabled in a RAID0 configuration, it is recommended to configure the storage controller cache for 100% read-cache, effectively disabling the write-cache.
The main consideration when utilizing RAID0 mode for storage controllers within Virtual SAN is the impact on the operational model. As mentioned above, RAID0 mode will require interaction with the storage controller software to manage the addition and removal of drives.
Performance and Sizing
Storage controller choice can have a significant impact on optimizing performance and or capacity sizing within your Virtual SAN cluster. Storage controller characteristics that impact performance include
- Storage controller interface speed
- Queue depth supported by the storage controller
- Number of drives supported per storage controller
A storage controller with a queue depth of greater than 256 is recommended for high Virtual SAN nodes.
Virtual SAN 5.5 supported Storage Controllers
The following is an early snapshot of storage controllers that will be listed within the VMware Compatibility Guide (VCG) upon the GA release of Virtual SAN. This does not circumvent validating final inclusion within the VMware Compatibility Guide, but is meant as a reference while Virtual SAN is still in beta. For hardware vendors that use equivalent vendor storage controllers to those certified to work with Virtual SAN(i.e. re-branded LSI controllers), the vendor specific equivalent controllers will be supported by Virtual SAN upon vendor initiated request.
- HP HBA H220i
- HP SMART Array p420i
- Dell PERC H200
- Dell PERC H310
- Dell PERC H710
- LSI 9207-8i
- LSI 9211-8i
- LSI 9240-8i
- LSI 9271-8i
Update : Now that Virtual SAN is GA, please see the VMware Compatibility Guide for the full list of supported storage controllers.