|Article Number: 534493||Article Version: 2||Article Type: Break Fix|
Dell EMC Unity Family
VMware ESXi datastore shows higher used space whereas on "Unity" side "Data reduction" is enabled.
Customer might have queries like below:
1. Why is the space utilization of the Datastore is different on Unity and VMware side.
2. Is compression working properly, if so, then why don't they see any savings on the Host side
3. What is the use of this "Data reduction" feature if host does not see any saving on his end.
VCenter will not be aware of the "Data savings " happening on Unity as it's a feature on Unity.
Allocation size : 570 GB
Current savings : 700 GB
This is because on Unity If the data is compressed, it must first be uncompressed before the data is sent to the host. If the compressed data already resides in System Cache, the data is uncompressed to a temporary location, the data is sent to the host, and the temporary location is released. If the compressed data being requested resides on disk, the data is first read into System Cache, uncompressed to a temporary location, and the host is sent the data. Data is never uncompressed on disk due to a read operation, as this would reduce the amount of savings on the storage resource.
Please go through the below document for Compression for more detailed explanation:
"Data reduction" is enabled while creating a "Datastore" on Unity
The array is working as per the design and needs no changes.
NOTE: In Dell EMC Unity OE version 4.3 and later, Dell EMC Unity Data Reduction replaces Dell EMC Unity Compression. Data reduction includes compression and deduplication logic within the space savings algorithm.