It is now very rare for a SAN to assign a LUN from contiguous disk space. Most SANS work with some form of track vector mapping. You should find out how the LUNS are assigned that you use for SQL Server.
With this approach, you only ever write and read a given track in the SAN. You never update anything.
When you want to update a track, the SAN gets a track from the free space pool and writes to that. When the write is complete, pointers are updated so that future reads use the new track instead of the old track.
If you have a SAN Snapshot in operation, the old track remains in the snapshot until the snapshot is deleted. When the track is no longer in use, it is put into a garbage pool for eventual recycling into the free space pool.
This approach is also what SSD drives do, but at the block level instead of the track level.
It makes very little difference to performance if your LUN is carved from contiguous space in te SAN or from vectorised storage - either can perform equally as well. However, vectorised storage can facilitate other operations, such as fast snapshots, fast file-level differential backups, etc, so it is the most widely used approach.
Original author: https://github.com/SQL-FineBuild/Common/wiki/ 1-click install and best practice configuration of SQL Server 2019, 2017 2016, 2014, 2012, 2008 R2, 2008 and 2005.
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