VNX snapshot What is VNX snapshot profile

VNX Snapshot is a new feature of the VNX for blocks OE release 5.32 that can be used for data backup, software development and testing, data validation, local fast recovery, and more.
Solution:

Profile

Currently, VNX Snapshot can only be used for pool LUNs, while raid Group LUNs only support Snapview Snapshot, because VNX Snapshot requires pool space as part of its technology implementation. SnapView snapshot is compatible with the pool LUN, which means that VNX snapshot and Snapview snapshot can coexist on the same pool LUN.

The VNX snapshot supports 256 writable Snap/pool LUNs, also supports branches (branching), snap snaps, branching without restrictions, as long as a primary LUN has no more than 256 snap totals. We also introduced the consistency group, which allows multiple pool LUNs to be placed in a consistency group and snap at the same time.

How does snapshot work?

VNX Snapshot uses the redirect on write (ROW) technique to redirect new write to the primary LUN to a different location in the pool, unlike copy on-I (COFW). (below) It is quite obvious that the VNX Snapshot is more concise for new write operations and is superior to Snapview Snapshot in performance.

Similarly, for read (below), VNX snapshot can read snapped Data from one location.

The granularity of each Vnx snapshot is 8KB, which means that each write occupies at least 8KB pool space. The distribution of 8KB block in 1GB Slice uses the same algorithm as the regular thin write. Let's take an example to see how Vnx snapshot is dealing with write.

First, the snap is created for the primary LUN, both pointing to the same data block (the following figure)

After that, the a block of the Primary Lun was modified to a ', the first snap still points to the original a,b,c,d, and if we do a Snap2 at this point, it will point to a ', b,c,d. When the next write modifies D->d ', then Primarylun will point to a ', b,c,d '.

Snapshot Mount Point (SMP)

SMP is a virtual lun-like container that simulates a regular LUN that enables the host to write to snapshot and provides the ability to change snapshot without having to rescan the SCSI bus. The other snapshot is loaded onto the SMP. SMP is created for the snapshot of a LUN, that is, each SMP can only be used by the snapshot of a single primary LUN. To enable the host to access snapshot, SMP must be added to storage Group, just like a regular LUN.