File locality

Introduction

For a distributed storage system one often has to use different file access scenarios for writing and reading. This section was created to provide necessary information about such scenarios and required storage system configurations.

Scenarios

• Scenario 0.0:

Dataset is randomly distributed among several sites without replicas.

Setting (attr ls /path_to_datacatalog):

sys.forced.nstripes="1"

• Scenario 0.1:

Dataset is randomly distributed among several sites with one replica (mirror).

Setting (attr ls /path_to_datacatalog):

sys.forced.nstripes="2"

• Scenario 1.0:

Dataset is located as close as possible to the specified region without replicas.

Setting (attr ls /path_to_datacatalog):

sys.forced.group="0"
sys.forced.placementpolicy="gathered:RU"
sys.forced.nstripes="1"

You can change the group number from 0 to $N, and geotag from RU to $YOUR_GEOTAG, but You should have FST with $YOUR_GEOTAG in group group.$N.

• Scenario 1.1:

Dataset is located as close as possible to the specified region with one replica on same region (mirror).

Setting (attr ls /path_to_datacatalog):

sys.forced.group="0"
sys.forced.placementpolicy="gathered:RU"
sys.forced.nstripes="2"

You can change the group number from 0 to $N, and geotag from RU to $YOUR_GEOTAG, but You should have FST with $YOUR_GEOTAG in group group.$N.

• Scenario 1.2:

Dataset is located as close as possible to the specified region with one replica as scattered as possible (mirror).

Setting (attr ls /path_to_datacatalog):

sys.forced.group="0"
sys.forced.placementpolicy="hybrid:RU"
sys.forced.nstripes="2"

You can change the group number from 0 to $N, and geotag from RU to $YOUR_GEOTAG, but You should have FST with $YOUR_GEOTAG in group group.$N.

• Scenario 2.0:

Dataset is located as close as possible to the client.

• Scenario 2.1:

Dataset is located as close as possible to the client with 1 replica (mirror).

• Scenario 3.0:

Dataset is located at sites of a single region.

• Scenario 3.1:

Dataset is located at sites of a single region with 1 replica (mirror).

Geotags

Geotag for FST (file /etc/sysconfig/eos_env):

EOS_GEOTAG="Country_code::sitename::rack"

Examples:

EOS_GEOTAG="RU::PNPI"

OR

EOS_GEOTAG="UK::RAL::rack1"

Groups

-- AndreyZarochentsev - 2018-05-23