Sorry for trouble again, not sure if this is correct category, moving this discussion from vCenter to vSphere.
hope get some help from you.
Hi, All
There is one question regarding VMware snapshot technology - CoW or RoW, confusing me for a long time, hope someone can help clarify this.
As we know that the difference between CoW and RoW is the location the changed data is written after a snapshot, like the snapshot space or original data area, for CoW, the changed data will be written to original data area instead of snapshot space after original data to be changed is copied to snapshot space, and for RoW, the changed data will be written to the space stores.
When take a snapshot for VMware, it creates some files, like delta disk files, .vmsd file, for delta disk files, it's a snapshot file and will store the changed data since last snapshot. So from this perspective, the snapshot technology VMware uses should be RoW, right?
However, from VMware guide or KB, we know that it uses CoW technology, as follows:
Understanding virtual machine snapshots in VMware ESXi and ESX (1015180) | VMware KB
The child disk
The child disk, which is created with a snapshot, is a sparse disk. Sparse disks employ the copy-on-write (COW) mechanism, in which the virtual disk contains no data in places, until copied there by a write. This optimization saves storage space. The grain is the unit of measure in which the sparse disk uses the copy-on-write mechanism. Each grain is a block of sectors containing virtual disk data. The default size is 128 sectors or 64 KB.
In addition, can anyone help explain the following snapshot chain regarding how it forms?
thanks
walker