Describe and differentiate technologies used in conjunction with a Distributed Storage Fabric, including snapshots, clones, high availability and disaster recovery
Snapshots + Clones
- DSF provides native support (VAAI, ODX, etc)
- Leverage redirect-on-write algorithm
- VM data consists of files (vmdk/vhdx) which are vDisks
- Snapshot taken = vDisk marked immutable
- New vDisk created as read/write
- Both vDisks have same block map
- Metadata mapping to corresponding extents
- Since each vDisk is its own block map, it eliminates need for snapshot chain
- When VM/vDisk is cloned, current block mapped is locked
- Clones created
- Previously cloned VM acts as “base disk”
- Clones from base VM have their own block map
- New writes/updates occur there
App Consistent Snapshots
- Native VSS for queiscing included
- VmQueisced Snapshot Service (Windows +
Linux)
- Post-free: /sbin/pre_freeze
- Post-thaw: /sbin/post_thaw
Eliminating ESXi Stun:
- When delta disks are created, ESXi
“stuns” the VM in order to remap disks to new deltas.
- Also occurs when snapshots are
deleted.
- During this process, OS cannot execute
operations (stuck)
- Duration depends on number of VMDK’s,
speed of datastore, etc.
- Nutanix VSS bypasses VMware
snapshot/stun process = more efficient
Shadow
Clones
- Distributed caching of vDisks/VM data in multi-reader scenario
- Ex. VDI deployment with many linked clones
- Read requests forwarded to “base VM”
- Read requests occur from more than two remote CVM’s (all read I/O) = vDisk marked immutable
- vDisk then cached locally by each VM
- Allows for each node to have a “base VM”