1. Proposal for the LHCb Italian Tier-2
Domenico Galli, Bologna
INFN CSN1
Roma,

2. Proposal for the LHCb Italian Tier-2. 2
Aim of LHCb Tier-2s
In the LHCb Computing Model Tier-2s are used for Monte Carlo production.
In the LHCb Computing Model Analysis is not performed on Tier-2s.
A LHCb Tier-2 consists in a PC-farm with a small disk buffer (3 TB in steady state) used as a temporary cache until data transfer to Tier-1.
LHCb-Italy proposes to build 1 Tier-2 hosted at Bologna-CNAF, together with Italian Tier­1.
In previous presentations these Tier-2 resources were kept together with Tier-1 resources; now, following referees’ suggestion, they have been kept apart since they have to be approved by CSN1.
Proposal for the LHCb Italian Tier-2. 2
Domenico Galli

3. Why LHCb Analysis at Tier-1?
LHCb analysis jobs consist in selecting the events (stripped DST) stored at Tier-1 to focus on one particular analysis channel:
Typical analysis jobs run on a ~106 event sample.
Some analysis jobs will run on a larger ~107 event sample.
Average event reduction of a factor of 5.
Analysis input is completely stored at each Tier-1.
Analysis output ( GB) can be processed by a small Tier-3 facility.
Available at each Tier-1
Available at each Tier-1
Selected DST+RAW 119 TB
Event Tag Collection 20 TB
Physics Analysis
n-tuple / User DST + User TAG Typical: 20 GB Large: 200 GB
Local Analysis
Proposal for the LHCb Italian Tier-2. 3
Domenico Galli
Paper

4. Why LHCb Analysis at Tier-1? (II)
Comparison between 2 models:
Analysis job at Tier-2:
Analysis job at Tier-1:
Data accessed at Tier-1 per analysis job are the same.
But the second is faster and less expensive in terms of hardware, infrastructure, staff resources and WAN load.
Tier-1
Tier-2
DST+RAW+TAG 139 TB
Buffer
Output GB
139 TB
WAN
LAN
Tier-1
DST+RAW+TAG 139 TB
Output GB
139 TB
LAN
Proposal for the LHCb Italian Tier-2. 4
Domenico Galli

5. Why LHCb Analysis at Tier-1? (III)
This model would allow maximum flexibility in moving resources back/forth between Tier-2 and Tier-1 to optimize resource exploitation.
E.g.: resources can be moved from Tier-2 to Tier-1 to satisfy peak analysis request, or vice versa in case on peak Monte Carlo request.
In this sense the distinction between Tier-1 and Tier-2 LHCb resources evaporates…
Proposal for the LHCb Italian Tier-2. 5
Domenico Galli

6. Overview of Italian LHCb Computing Resources
CNAF
LAN
LHCb Tier-3
WAN
Tier-1
(reconstruction, stripping, analysis)
LHCb Tier-2
(Monte Carlo)
Gateway
Proposal for the LHCb Italian Tier-2. 6
Domenico Galli

7. LHCb Tier-2 Size and Cost
We are sizing the Italian Tier-2 to be 15% of the total Tier-2 resources of the whole LHCb collaboration.
15% = Italian fraction of CORE funds
15% = fraction of Italian physicists with respect of the total involved in the LHCb experiment.
Proposal for the LHCb Italian Tier-2. 7
Domenico Galli

8. LHCb Tier-2 Size and Cost (II)
Strictly according to current LHCb Computing Model
2006
2007
2008
2009
2010
total
CPU [€/Si2k]
0.58
0.38
0.25
0.17
0.12
Disk [€/GB]
2.25
1.40
0.88
0.55
0.34
CPU running [MSi2k]
0.69
1.15
Disk running [TB] 1 2 3
CPU replacement [MSi2k]
0.35
Disk replacement [TB]
CPU to be acquired [MSi2k]
0.46
Disk to be acquired [TB]
CPU cost [k€]
196.5
132.4
117.1
56.1
43.3
545.5
Disk cost [k€]
2.2
1.4
0.9
0.5
0.3
5.4
Total cost [k€]
198.7
133.8
118.0
56.7
43.7
550.9
Proposal for the LHCb Italian Tier-2. 8
Domenico Galli

9. LHCb Tier-2 Size and Cost (III)
However the Computing Model is not Bible!
It is only a raw estimate of the needs, based on today knowledge and understanding.
If additional resources will be available in the forecoming years for the LHCb Tier-2, these could result precious.
Furthermore these resources could be moved back and forth to/from Tier-1 on need, to allow most optimized usage.
Proposal for the LHCb Italian Tier-2. 9
Domenico Galli