Difference between revisions of "ALICE native xrootd"
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== Aim of this documentation == | == Aim of this documentation == | ||
Version du 10:57, 18 novembre 2015
Decommissioning ALICE native xrootd servers and dealing with data loss
Aim of this documentation
This objective of this document is to detail the procedure to follow by system administrators when they want to remove an xrootd server (decommissioning) or when they lost a filesystem on an xrootd server.
This document is based on the mails exchanged on the alice-lcg-task-force@cern.ch list and on the real cases encountered at the GRIF-IPNO site. Costin Grigoras is the author of the different recommendations and tips successfully applied at IPNO.
About the examples
The examples are taken from the IPNO sites where the redirector is ipngridxrd0.in2p3.fr and the xrootd servers are ipngridxrd1, ipngridxrd2, ... On all the xrootd servers the data partitions mount points follow the same naming convention: the data partitions are /grid/xrddataX {X=1..8}.
A quick presentation of the xrootd files tree
On each xrootd server there are on or more disk partitions where the data files are stored. There is also a namespace which is a directory containing the names of the data files: theses names are the ones the redirector uses. The name itself is a symlink to the real data file. The name space can be in a separate partition or in a subdirectory of a data partition.
In the case of IPNO, the namespace is always a subdir of the first data partition. Here are some example from one xrootd server:
# df -h|grep xrddata /dev/sdb1 9.1T 5.6T 3.6T 62% /grid/xrddata1 /dev/sdb2 9.1T 5.6T 3.6T 62% /grid/xrddata2 /dev/sdb3 9.1T 5.6T 3.6T 62% /grid/xrddata3 /dev/sdb4 9.1T 5.6T 3.6T 62% /grid/xrddata4 /dev/sdc1 9.1T 5.6T 3.6T 62% /grid/xrddata5 /dev/sdc2 9.1T 5.6T 3.6T 62% /grid/xrddata6 /dev/sdc3 9.1T 5.6T 3.6T 62% /grid/xrddata7 /dev/sdc4 9.1T 5.6T 3.6T 62% /grid/xrddata8 # # ls -ld /grid/xrddata1/namespace drwxr-xr-x 18 xrootd xrootd 4096 Mar 30 2015 /grid/xrddata1/namespace </tt> The data file %grid%xrddata1%namespace%00%65278%b8f9f574-dd42-11e4-a4e6-63e8b3f6492f in the partion /grid/xrddata6 is recorded in the namespace as /grid/xrddata1/namespace/00/65278/b8f9f574-dd42-11e4-a4e6-63e8b3f6492f : <pre> # ls -lh /grid/xrddata1/namespace/00/65278/b8f9f574-dd42-11e4-a4e6-63e8b3f6492f lrwxrwxrwx 1 xrootd xrootd 85 Apr 7 2015 /grid/xrddata1/namespace/00/65278/b8f9f574-dd42-11e4-a4e6-63e8b3f6492f -> /grid/xrddata6/%grid%xrddata1%namespace%00%65278%b8f9f574-dd42-11e4-a4e6-63e8b3f6492f # ls -lLh /grid/xrddata1/namespace/00/65278/b8f9f574-dd42-11e4-a4e6-63e8b3f6492f -rw-rw-r-- 1 xrootd xrootd 3.6M Apr 7 2015 /grid/xrddata1/namespace/00/65278/b8f9f574-dd42-11e4-a4e6-63e8b3f6492f
To access the file in this example, the URL will be root://ipngridxrd0.in2p3.fr:1094//00/65278/b8f9f574-dd42-11e4-a4e6-63e8b3f6492f where ipngridxrd0 is the redirector here. For example to copy the file from a WN:
# xrdcp root://ipngridxrd0.in2p3.fr:1094//00/65278/b8f9f574-dd42-11e4-a4e6-63e8b3f6492f /tmp/xrd_test.dat [3.594MB/3.594MB][100%][==================================================][3.59 [3.594MB/3.594MB][100%][==================================================][3.594MB/s] [root@ipngrid90 ~]# ls -lh /tmp/xrd_test.dat -rw-r--r-- 1 root root 3.6M Nov 18 10:54 /tmp/xrd_test.dat [root@ipngrid90 ~]# rm /tmp/xrd_test.dat
