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Review: VMware VSAN turns storage inside-out

Paul Ferrill | Aug. 21, 2014
VMware's Virtual SAN 1.0 combines easy setup and management with high availability and high performance -- and freedom from traditional storage systems

Number of disk stripes per object. This value defines the number of physical disks across which each replica of a storage object is striped. It defaults to one. Setting this value to greater than one might increase performance (when a request results in a cache miss), but it's not guaranteed.

Flash read cache reservation. This is the amount of flash capacity reserved on the SSD as read cache for the storage object with a default of zero. The VSAN scheduler handles cache allocation by default, although it is possible to increase the amount on an object basis to address performance issues.

Object space reservation. VSAN uses a thin-provisioning model for all objects with a specific amount reserved upon first initialization. The value for this setting is expressed as a percentage of the logical size of the object and will differ depending on the object. The value for VM swap defaults to 100 percent to reserve the full amount, while the value for virtual machine disks defaults to zero.

Force provisioning. This setting allows you to provision a storage object even if the policy requirements are not met by the VSAN data store (such as when the number of available nodes is no longer sufficient to meet the object's high-availability requirements).

Installing VSANCreating a VSAN cluster is simply the last step in creating a vSphere cluster and amounts to clicking a check box in vCenter Server. Of course, if you're starting completely from scratch, as I did, you'll need to install vSphere and vCenter.

For the initial boot and installation of vSphere/ESXi, I used the Supermicro IPMI management console and connected the VMware .ISO file as a remote media drive. Next, I installed to a USB key and repeated the process on the additional three nodes. The Supermicro box has a SATA Disk On Module in addition to an internal USB port for use as a boot device. The Lenovo servers have DVD drives along with USB.

One side effect of using all locally attached drives with VSAN is that you won't have any drives to use for a data store until you have the VSAN cluster up and running. With vSphere 5.5, you must use vCenter Server for all cluster management tasks, which poses a chicken-and-egg issue. I ended up using a Thecus N7710-G NAS storage box, which provides both iSCSI and NFS, as an external source until I got the VSAN cluster up and running.

One of the requirements for VSAN is that each disk drive must be individually addressable. For some controllers, this involves a simple setting to enable pass-through mode. However, for the Supermicro nodes, I had to use the LSI controller firmware to create individual drive groups for each drive and set the reliability to none. This RAID 0, single-drive configuration had to be accomplished for each of the five 2TB drives and the SSD on all four nodes. The process was essentially the same for the Lenovo nodes.


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