Configuration of RAO in CTA

Introduction

This page will explain how to configure the Recommended Access Order (RAO) on CTA.

There are two types of RAO:

• Enterprise RAO
• CTA RAO (from the CTA version v3.1-7)

The configuration of RAO in CTA

In order to enable the RAO on a tapeserver, the configuration file located in /etc/cta/cta-taped.conf has to be filled properly.

Enable or not RAO

To enable RAO on a tapeserver the UseRAO configuration line has to be set to yes:

# Use Recommended Access Ordering if available
taped UseRAO yes

To disable RAO on a tapeserver, set the UseRAO configuration line has to be set to no.

# Use Recommended Access Ordering if available
taped UseRAO no

Configuration parameters for RAO

Only for LTO drives, the following two lines can be modified on the /etc/cta/cta-taped.conf file to set the RAO Algorithm to use:

taped RAOLTOAlgorithm rao_lto_algorithm_name_to_use
taped RAOLTOAlgorithmOptions option1_name:option1_value,option2_name:option2_value

The different RAO algorithms

Modify the /etc/cta/cta-taped.conf file to setup the RAO algorithm to use.

Enterprise RAO algorithm

Warning

This algorithm will only be executed on enterprise drives.

This algorithm simply asks the drive to perform its internal RAO algorithm.

# Use Recommended Access Ordering if available
taped UseRAO yes

Linear RAO algorithm

Warning

This algorithm will only be executed on LTO drives.

This algorithm will order by FSeq the files to retrieve

# Use Recommended Access Ordering if available
taped UseRAO yes
taped RAOLTOAlgorithm linear

Random RAO algorithm

Warning

This algorithm will only be executed on LTO drives.

This algorithm will randomly order the Fseq of the files to retrieve.

# Use Recommended Access Ordering if available
taped UseRAO yes
taped RAOLTOAlgorithm random

Short Locate Time First (SLTF) RAO algorithm

Warning

This algorithm will only be executed on LTO drives.

This RAO algorithm is explained here: LTO performance, Make Tape Reading Great Again

Before configuring this RAO algorithm, the LTO tapes media type should have the following informations provided:

• The minimum longitudinal position (minLpos)
• The maximum longitudinal position (maxLpos)
• The number of wraps the media contains (nbWraps)

If these informations are not provided, the linear RAO algorithm will be executed.

# Use Recommended Access Ordering if available
taped UseRAO yes
taped RAOLTOAlgorithm sltf
taped RAOLTOAlgorithmOptions cost_heuristic_name:cta

If these configuration lines are incorrectly entered, the linear RAO algorithm will be executed.

Summary of the selection of the RAO algorithm to execute by the tapeserver

The following image summarize which RAO algorithm will be executed by the tapeserver according to the drive type and the configuration provided in the /etc/cta/cta-taped.conf file.