Fast VP vs Fast Cache

I saw many interviews that ask this question - whats the difference between Fast VP and Fast Cache?

FAST Cache:

A FAST Cache is literally a High Speed Disks which acts a Cache Disk in EMC Storages. Basically it's a Flash Disk, which you can combine together through a small wizard via Unisphere and can configure the FAST cache. 

The basic purpose of FAST cache is to deliver the most HOT data at an instant or we can say that the data which is most hit on any LUN gets transfer to the FAST cache and hence the data get accessed from there, delivering more IOPS.


NOTE- These are a combination of Disk of same type flash Disk SSD which are basically SLC type

FAST VP:

Fast VP is a  Group of Disk (may consist of different type of SSD's like Flash,SAS,NL-SAS) to create a Storage Pool and the HOT data is moved across the disks after analysis over a period of time.


Think like this 

4 Flash SSD + 4 SAS + 2 NL-SAS = Extreme Performance (pool)
4 Flash SSD + 2 SAS + 2 NL-SAS = Balanced Performance (pool)
1 Flash SSD + 2 SAS + 4 NL-SAS = Capacity Performance (pool)

It allows you to create multiple storage Pools so that you can get the maximum out of any SSD and also the most frequent data after analysis moved to Flash disk. 

NOTE- FAST VP Flash SSD's are eMLC's,they cannot sustain high IOPS hence cannot be used as FAST Cache disks


Difference between FAST CACHE and FAST VP

FAST CACHE	FAST VP
Allows Flash drives to be used to extend the existing caching capacity of the whole storage system	Allows a single LUN to leverage the advantages of multiple drive types through the use of storage pools.
Granularity is 64 KB	Granularity is 1 GB
Data that is accessed frequently is copied from HDDs to Flash drives	Data is moved between different storage tiers based on statistics collected over a period of time
Use when workload changes are unpredictable and very dynamic, and require a quick response time	Use when workload pattern changes are predictable and relatively low.
Constantly promotes frequently accessed HDD data to FAST Cache. There are no relocation cycles.	Data movement occurs in scheduled or manually invoked relocation windows
Calculation to decide which data needs to be promoted to FAST Cache is performed continuously.	Calculation to decide which portion of data need to be moved is performed once every hour.

If you want more indepth details you can refer to below link:

http://tinyurl.com/zn9h7vq

Let me know if you have any Questions.. Happy reading