Introduction

This page briefly explains what the ATLAS computing model is, what facilities are avaliable at RAL and how ATLAS users can access them.

The ATLAS computing Model

The RAW data is produced by ATLAS at CERN, this is referred to as the Tier 0. The data is archived at CERN before being distributed to the Tier 1s. There are 10 Tier 1s serving ATLAS. RAL is the UK Tier 1 and is expected to recieve 10% of the raw data from CERN. Each Tier 1 has several Tier 2 sites asscoiated with it. The job of the Tier 1 is to re-process and distribute the data around the Tier 2s. The job of the Tier 2s is to run user analysis on the data. Finally there are so called Tier 3 sites. These sites do not hold any official copies of ATLAS data but individuals can copy data to them in order to run their own analysis.

Tier 1

The Tier 1 for the UK cloud is based at RAL. The Tier 1 is in the machine room in building R89. In order to run at the Tier 1 your grid certificate must be either: /atlas/uk/Role=production /atlas/uk/Role=poweruser0 The avaliable space tokens are

Space Token	Permission	Notes
RAL-LCG2_MCDISK	default
RAL-LCG2_DATADISK	default
RAL-LCG2_HOTDISK	default	Used to store an extra copy of "hot" data
RAL-LCG2_SCRATCHDISK	default + poweruser0 get write permission	Deleted after 28 days
RAL-LCG2_MCTAPE	default	Disk buffer for the MC tape
RAL-LCG2_DATATAPE	default	Disk buffer for the Data tape

The default permissions is read and write for production and read permission for poweruser0. The group disks that were avaliable at the Tier 1 are being removed in favour of the scratch disk.

The full list of the space tokens available on the grid can be found at Tiers of ATLAS

Tier 2

As well as the Tier 1 there is a Tier 2 cluster also based at RAL however it is in a different building from the Tier 1 and run by different people.

Space Token	Permission	Notes
RALPP_MCDISK	default
RALPP_DATADISK	default
RALPP_HOTDISK	default	Used to store an extra copy of "hot" data
RALPP_PRODDISK	default
RALPP_SCRATCHDISK	default + everyone get write permission	Deleted after 28 days
RALPP_SOFT-TEST	default + soft-test users get write and delete permission
RALPP_LOCALGROUPDISK	default + UK users get write permission

The default permissions is read and write for production and read permission for poweruser0 and normal users.

Local Cluster / Tier 3

The Tier 3 is actually part of the Tier 2 that has been reserved for use by RAL staff.

Disk	Size	Backed Up	Usage
$HOME	1 GB*	Yes	Personal files
/opt/ppd/atlas	128 GB	Mirrored every 12 hours	ATLAS group usage
/opt/ppd/scratch	1.6 TB	No	Data - An email will be sent reminding you to delete files
/opt/ppd/month	1.6 TB	No	Data - An email will be sent reminding you to delete files

*The initial allowance is 2MB but this is a soft cap and will be removed if you send an email to Chris Brew.

As well as access to local disk space RAL users will also have access to the space tokens avaliable on the Tier 2.

Information on how you can access the grid storage element can be found here

-- AlastairDewhurst - 2009-10-09