Virtual Storage Tier – VST

An insight into Virtual Storage Tier – VST

A few questions answered regarding VST

1. Is there data migration involved?

No. Any time a read request is received for a block on a volume or LUN where the VST is enabled, that block is automatically subject to promotion. The promotion of a data block to the VST is not data migration because the block remains on hard disk media when a copy is made to the VST.

2. Does this require additional disk I/O?

With the VST, data is promoted to Flash media after the first read from hard disk drives. This approach to data promotion means that additional disk I/O operations are not needed to promote hot data.

 3. How is this achieved?

NetApp algorithms distinguish high-value data from low-value data and then retain that data in the Virtual Storage Tier. NetApp metadata, is always promoted when read for the first time. In contrast, sequential reads are normally not cached in the VST unless specifically enabled because they tend to crowd out more valuable data.

It is possible to can change the behaviour of the intelligent cache to meet the requirements of applications with unique data access requirements. For example, VST can be configured to cache incoming random writes as they are committed to disk and to enable the caching of of sequential reads.

It is possible to create different classes of service by enabling or disabling the placement of data into the VST on a volume-by-volume basis.

4. How does VST differ from other implementations?

Other implementations may not promote hot data until it has been read from disk many times, and then additional disk I/O is still required to accomplish the promotion process.

5. What is the block size used?

4KB block

6.  How does it enhance system performance?

Because only hot data blocks are promoted and because data does not have to be moved back to the original tier when it becomes cold, the requirement for data movement is eliminated. This reduces the processing burden on system resources and reduces traffic in the disk subsystem.

 7. How is it installed and configured?

To deploy the NetApp Virtual Storage Tier, simply install Flash technology in your storage systems. Once this is accomplished, the Virtual Storage Tier becomes active for all volumes managed by the storage controller. It is possible to exclude user data for lower-priority volumes from the Virtual Storage Tier if required.

 8. What is cache amplification?

When a volume is enabled for deduplication, the benefits of deduplication persist in the Virtual Storage Tier. A single block in the Virtual Storage Tier could have many metadata pointers to it, increasing the probability that it will be read again and thus increasing the value of promoting that block . With this cache amplification a single block in the Virtual Storage Tier can serve as several logical blocks.

VST Portfolio

1.      1.  Flash Accel (Server level) – PCI-e flash and SSD devices on server to be used as server cache.

a.       Accelerates specific applications

b.      Supports VMware vSphere

c.       Managed by software installed on server

2.      2. Flash Cache (Controller level)

a.       Highest performance for file  services

b.      Improves latency for random reads

c.       Easiest way to add Flash

d.      Delivers predictable, high speed data across

3.      3.  Flash Pool (Disk Shelf level)

a.       Highest performance for OLTP

b.      Accelerates random reads and writes

c.       Automates the use of SSD technology

Reference

White Paper: WP-7127 –  The NetApp Virtual Storage Tier

 

 

 

 

1.       Flash Accel (Server level) – PCI-e flash and SSD devices on server to be used as server cache.

a.       Accelerates specific applications

b.      Supports VMware vSphere

c.       Managed by software installed on server

2.       Flash Cache (Controller level)

a.       Highest performance for file  services

b.      Improves latency for random reads

c.       Easiest way to add Flash

d.      Delivers predictable, high speed data across

3.       Flash Pool (Disk Shelf level)

a.       Highest performance for OLTP

b.      Accelerates random reads and writes

c.       Automates the use of SSD technology

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