7.3.2.2 Objects and Components
A vSAN object represents a logical block device, typically associated with SCSI block storage. For example, a virtual disk (VMDK), VM swap, and the VM home namespace are all objects. Objects are distributed across the vSAN cluster using components. There are replica components which are full copies of the data, such as the VMDK disk, and witness components that contain only metadata for the object.
RAID1 (Mirroring) will be used in any examples that follow since it offers the best performance. When this mode is used, there is one witness component per object, and a number of replica components that will depend on the FTT (Failures to Tolerate) configuration.
The maximum size of a single component is 255GB, therefore if an object is larger than 255GB, it is split into multiple components. The table below lists the objects for a virtual machine:
Table 11. vSAN Objects
Object | Description |
Virtual machine home namespace | VM Configuration (.vmx), log files, and digest files. |
Virtual machine swap | Virtual machine swap is equal to the amount of configured VM memory, minus any reservations. Only applies to powered-on virtual machines. |
Virtual machine disk (VMDK) | OS VMDK, OS Checkpoint, user data disk, disposable disk, Linked Clone internal disk, App Volumes mounted AppStack, App Volumes Writeable Volume. |
Snapshot deltas | Virtual machine snapshot delta files. |
Snapshot memory (.vmem) | Virtual machine memory snapshot used to retain the live state of a virtual machine. |
Redo-log file | Redo-log files are used with independent non-persistent disks, and are present in the virtual machine name space. App Volumes AppStacks are independent non-persistent (read-only) VMDK objects, with each AppStack mount (concurrent user) requiring a redo-log file object. |
By default, virtual swap is provisioned with 100% Object Space Reservation, however, as of VSAN 6.2 virtual swap can be thin provisioned using the SwapThickPrivisionDisabled setting.
Note By default, Horizon uses a replica disk policy that has a read cache reservation of 10%. If an all-flash configuration is used, please refer to KB 2109890 (
https://kb.vmware.com/kb/2109890). All-flash configurations do not currently support the Flash Read Cache Reservation storage policy attribute, and is not supported.