Oracle FS1-2 Flash Storage System
 

PLA-Support>Sun Systems>DISK>Flash Storage>SN-EStor: FSx
 

In this Document

Goal

What is access skew ?

Access skew range :

How the skew value is determined :

Solution

Method using FS System Manager GUI

Method using FS System Manager CLI (FSCLI)

References

Applies to:

Goal

What is access skew ?

LUNs and Storage Domains are constructed from a collection of data blocks. Data access occurs across these data blocks and is characterized by a particular statistical pattern.
The degree of asymmetry in the statistical distribution of the block accesses for a LUN is called access skew.

The skew value for a LUN helps to determine the effectiveness of QOS plus on that particular LUN.

Volumes that have a large number of access requests that are skewed to a relatively small portion of the user data benefit the most from the features of QoS Plus.

Access skew range :

The FS1 calculates access skew in a range of 0 to 100 for comparative purposes.
When all the blocks in all the LUNs are accessed uniformly, auto-tiering has no hot data to place on the high performance storage, and no cold data to place on the low-cost storage.

Pure random access is an example of zero skew because all data blocks are accessed equally.
Pure sequential access is another example of zero skew as each data block is accessed only once.

An access skew of 100 indicates a limited number of data blocks accounting for all the data accesses.
This situation can be characterized as an unfair data access pattern, because a limited number of data blocks account for virtually all the accesses.

Auto-tiering is at its best when access patterns are unfair resulting in a skew value that is rewarded with the highest performing storage class.

How the skew value is determined :

The Oracle FS System monitors,collects and analyzes the data activity statistics of the LUN to determine if the initial properties make the best use of the available storage resources.
For a LUN that is using QoS Plus, the Oracle FS System gathers and stores statistics about the access requests as I/O is performed on the LUN.

When optimizing for system performance, QoS Plus moves frequently accessed data blocks of a LUN to a faster, more expensive Storage Class, such as highperformance solid-state drives (SSDs).

Conversely, when optimizing for cost, QoS Plus moves infrequently accessed data blocks to a slower, less expensive Storage Class, such as high-capacity hard disk drives (HDDs).

Solution

How to find the skew value for each LUN ?

Method using FS System Manager GUI

Generate Auto Tier Effectiveness Report :

1. Navigate to System > Storage Domains.
2. Select the Storage Domain to report.
3. Select Actions > Generate Auto-tier Effectiveness Report.
4. (Optional) Update a value in the Storage Costs table.
5. To update a value, double-click the cell.
6. Generate the report.

Look at the value for "Constrained skew".

It indicates the degree of uniformity of the data distribution and the I/O activity across all of the Storage Classes that are available to the auto-tiered LUN.
The report provides a value between 0 and 100.

Method using FS System Manager CLI (FSCLI)

Look at "Skew" value. The report provides a value between 0 and 100.

For both GUI and CLI,

• If the skew value is close to "100" indicates unfair data access and QoS Plus can benefit the LUN.
• If the skew value is close to "0" indicates that the I/O activity and data are evenly distributed across all of the available Storage Classes. QoS Plus can provide little benefit for the LUN.

You can find the skew value for LUNs from the FS1-2 log bundle by executing script FSInfo.pl -l. Look at values under column Skew.

Or else from the *.chsh.xml or SystemConfiguration.txt files.

This solution has no attachment