RSE Expressions

An RSE Expression allows to select a set of RSEs, for example to create replication rules. The RSE Expression consists of one or more terms. A term can be a single RSE name or a condition over the RSE attributes. The RSE Expression Parser resolves each term to a set of RSEs. Terms can be connected by operators to form more complex expressions. For example, users can write RSE expressions to address all Tier 2 RSEs, all the RSEs in certain cloud, all Tier 2 RSEs not in certain clouds, etc.

Simple RSE Expressions

Rucio allows to test RSE Expressions, using the command list-rses. The most simple RSE Expression is the one containing the name of a particular RSE.

1. The following expression returns all RSEs:

   jbogadog@lxplus0058:~$ rucio list-rses --expression '*'
   IFIC-LCG2_LOCALGROUPDISK
   IFAE_PRODDISK
   PIC_SCRATCHDISK
   EELA-UNLP_SCRATCHDISK
   CERN-PROD_TZDISK
   BNL-OSG2_MCTAPE
   BNL-OSG2_DATADISK
   IN2P3-CC_MCTAPE
   CERN-PROD_DERIVED
   CERN-PROD_DATADISK
   EELA-UNLP_DATADISK
   UAM-LCG2_SCRATCHDISK
   IFIC-LCG2_DATADISK
   LIP-COIMBRA_LOCALGROUPDISK
   ...
   

2. Whereas the next expression only returns a set containing a single RSE:

   jbogadog@lxplus0058:~$ rucio list-rses --expression EELA-UNLP_SCRATCHDISK
   EELA-UNLP_SCRATCHDISK
   

3. Another simple RSE Expression allows to list the set of all the RSEs in a particular site:

   jbogadog@lxplus0058:~$ rucio list-rses --expression site=EELA-UNLP
   EELA-UNLP_PRODDISK
   EELA-UNLP_DATADISK
   EELA-UNLP_SCRATCHDISK
   

4. Or all the RSEs who’s type is SCRATCHDISK:

   jbogadog@lxplus0058:~$ rucio list-rses --expression type=SCRATCHDISK
   UNI-SIEGEN-HEP_SCRATCHDISK
   NCG-INGRID-PT_SCRATCHDISK
   EELA-UNLP_SCRATCHDISK
   ...
   INFN-T1_SCRATCHDISK
   FMPHI-UNIBA_SCRATCHDISK
   INFN-FRASCATI_SCRATCHDISK
   

5. Or all the Spanish sites:

   jbogadog@lxplus0058:~$ rucio list-rses --expression SPAINSITES
   IFIC-LCG2_LOCALGROUPDISK
   IFAE_PRODDISK
   PIC_SCRATCHDISK
   EELA-UNLP_SCRATCHDISK
   ...
   EELA-UNLP_DATADISK
   UAM-LCG2_SCRATCHDISK
   IFIC-LCG2_DATADISK
   LIP-COIMBRA_LOCALGROUPDISK
   

6. Also numerical comparisons with < and > are possible:

   jbogadog@lxplus0058:~$ rucio list-rses --expression "freespace>3000"
   CERN-PROD_TZDISK
   BNL-OSG2_MCTAPE
   BNL-OSG2_DATADISK
   IN2P3-CC_MCTAPE
   CERN-PROD_DERIVED
   CERN-PROD_DATADISK
   

Note that if the RSE Expression returns an empty set, Rucio returns an error as an RSE Expression must resolve to at least one RSE. Thus, an error does not necessarily mean that the syntax of the expression is wrong, it might just result into an empty list.

In 3) and 4), the RSE Expression refers to an attribute in the RSE that must be equal to a given value to match the expression. While in 2) and 5), the expression matches an RSE if the attribute is True. In 6) a numerical term is used to resolve all RSEs with more than 3000 TB free space. It is possible to see the list of attributes for a particular RSE with Rucio:

jbogadog@lxplus0100:~$ rucio list-rse-attributes EELA-UNLP_SCRATCHDISK
  ftstesting: https://fts3-pilot.cern.ch:8446
  ALL: True
  ESTIER2S: True
  physgroup: None
  spacetoken: ATLASSCRATCHDISK
  fts: https://fts3.cern.ch:8446,https://lcgfts3.gridpp.rl.ac.uk:8446,https://fts.usatlas.bnl.gov:8446
  site: EELA-UNLP
  EELA-UNLP_SCRATCHDISK: True
  datapolicyt0disk: False
  cloud: ES
  SPAINSITES: True
  datapolicyt0taskoutput: False
  fts_testing: https://fts3-pilot.cern.ch:8446
  tier: 3
  datapolicyt0tape: False
  type: SCRATCHDISK
  istape: False

Most of the RSEs share the same set of attributes, and is possible to create RSE Expressions based on all of them.

Operators

Operators are used to connect terms in order to get more complex RSE Expressions/terms. The syntactic functionality of the Rucio RSE Expressions Parser allows the basic operations defined in mathematical set theory, Union, Intersection and Complement. Using an operator on two sets of RSEs will construct a new set based on the given sets.

The symbols A and B in this table stand for a term.

Operator	Meaning	Interpretation	Example
A|B	UNION	A union B	EELA-UNLP_SCRATCHDISK | EELA-UNLP_PRODDISK
A&B	INTERSECT	A intersect B	tier=1&country=us
A\B	COMPLEMENT	A complement B	cloud=ES\type=SCRATCHDISK

Composing RSE Expressions

Using the operators described above, it’s possible to create expressions to select whatever RSE you need to put your data in. Use the following list of examples to build your own RSE Expressions.

All Tier 2 sites in DE cloud:

jbogadog@lxplus0100:~$ rucio list-rses --expression 'tier=2&cloud=DE'
PRAGUELCG2_PPSLOCALGROUPDISK
FMPHI-UNIBA_LOCALGROUPDISK
...
UNI-FREIBURG_DATADISK
DESY-HH_PRODDISK

Note the use of the single quotes. Single quotes are needed to avoid the shell interpret the &, the | or the \ as commands.

All tier 1 but not the ones in country=us:

jbogadog@lxplus0100:~$ rucio list-rses --expression 'tier=1\country=us'
INFN-T1_MCTAPE
BNL-OSG2_DATATAPE
...
BNL-OSG2_DDMTEST
NIKHEF-ELPROD_PHYS-SUSY

However, take care of the subtle differences. While the first expression exclude United States’ sites, the second doesn’t:

jbogadog@lxplus0100:~$ rucio list-rses --expression 'tier=1\country=us'|wc -l
115
jbogadog@lxplus0100:~$ rucio list-rses --expression 'tier=1\country=US'|wc -l
117

The filters are processed from left to right. Is possible to use parenthesis to force the order of operation. See the following example to get all the SCRATCHDISKs in IT or FR clouds:

jbogadog@lxplus0100:~$ rucio list-rses --expression 'cloud=IT|cloud=FR&type=SCRATCHDISK'|wc -l
30
jbogadog@lxplus0100:~$ rucio list-rses --expression '(cloud=IT|cloud=FR)&type=SCRATCHDISK'|wc -l
30
jbogadog@lxplus0100:~$ rucio list-rses --expression 'type=SCRATCHDISK&(cloud=IT|cloud=FR)'|wc -l
30
jbogadog@lxplus0100:~$ rucio list-rses --expression 'type=SCRATCHDISK&cloud=IT|cloud=FR'|wc -l
92

While the first three operations are equivalent, the last return sites in cloud FR but not only the SCRATCHDISKs but the GROUPDISKs and DATADISKs too, among other types.