Difference between revisions of "DCache"
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== grid-ftp ==
== grid-ftp ==
Revision as of 16:17, 7 July 2016
dCache is filesystem designed for storing large amounts of data. The data is stored amongst many server nodes, accessed through a single virtual filesystem by a variety of methods. The dCache filesystem is available on stoomboot and can be found under the directory
There are no backups of made of the dCache file system.
Files written to dCache are fixed and not changeable, see #Immutable Files. Other than this limitation dCache can be used pretty much as a normal file system.
Issues and problems with the file system should be sent to
To get a storage directory created for yourself please send a request to
stbc-admin[AT]nikhef[DOT]nl. Please include
which group you are working with and where in the dcache directory hierarchy to create your directory as the directory organisation within
each group subdirectory is up to each group. And finally don't forget a name for the new directory.
dCache can be accessed from any of the stoomboot nodes, both the interactive and compute nodes. The file system is mounted via an nfs mount point
/dcache. This mount point is the same across all the stoomboot nodes. Running jobs can also read and write to dCache as jobs run under the identity of the user who submitted the job and so have the same access rights as the same user in an interactive shell. There is no access to the /dcache mount from outside stoomboot.
Once a file is written into dCache the contents of the file can not be changed.
This means a file CAN NOT be overwritten:
[stbc-i1 /dcache/test]$ echo 123 > test.file [stbc-i1 /dcache/test]$ echo 1234 > test.file -bash: test.file: Permission denied
and CAN NOT be appended to:
[stbc-i2 /dcache/test]$ echo 123 > test.file [stbc-i2 /dcache/test]$ echo 4 >> test.file -bash: test.file: Permission denied
and when deleting a file is always treated as being write protected (even if the writable bit is set):
[stbc-i2 /dcache/test]$ ll test.file -rw-r--r--. 1 andrewp datagrid 4 May 4 09:57 test.file [stbc-i2 /dcache/test]$ rm test.file rm: remove write-protected regular file `test.file'? y
These limitations mean that dCache is NOT suited for such things as compiling code on, storing large files being actively edited (e.g. word documents) or storing files under a version control system.
There are NO BACKUPS of files stored on the dCache file system.
Storage Space Organisation
The total storage space on the dCache storage nodes is about 550 TB. Each group has a directory under the main dcache directory:
[stbc-i4 ~]$ ll /dcache/ total 2 drwxr-xr-x. 4 root alice 512 Apr 1 11:46 alice drwxr-sr-x. 5 root atlas 512 May 4 09:48 atlas drwxrwsr-x. 3 root datagrid 512 Nov 13 2015 datagrid
User storage directories are under the appropriate group directory:
[stbc-i4 ~]$ ll /dcache/datagrid/ total 1 drwxr-sr-x. 1094 andrewp datagrid 512 May 4 09:59 andrewp
Storage space is assigned to each group under there group directory so all people within a group share the same group storage space allocation.
TO-DO: df doesn't give useful results for dcache so a web page with current data usage will be setup
Remote access to the dCache storage using grid certificate authorisation is being setup and is currently in the testing stage. To register your grid certificate for remote access please send your grid certificate's DN to
stbc-admin[AT]nikhef[DOT]nl with a request for remote access to dcache. To get the DN of a certificate from the certificate file, run the following command:
openssl x509 -in __cert_file__ -noout -subject
__cert_file__ with the file name of the certificate.
Once your certificate DN is registered as described above, the xrootd door can be accessed at
The directory paths are the same as for nfs access. So for example the directory
/dcache/test on stoomboot can
be seen via xrootd at
root://dcache.nikhef.nl/dcache/test. To list the directory use the command
[bosui ~]$ xrd dcache.nikhef.nl dirlist /dcache/test
And to copy a file:
[bosui ~]$ xrdcp test1 root://dcache.nikhef.nl/dcache/test/test1
Similarly to the xrootd door, once your certificate DN is registered as described above, the xrootd door can be accessed at
dcache.nikhef.nl. To list a directory use the command
globus-url-copy -list, for example:
[bosui ~]$ globus-url-copy -list gsiftp://dcache.nikhef.nl/dcache/test/
And to copy a file:
[bosui ~]$ globus-url-copy test1 gsiftp://dcache.nikhef.nl/dcache/test/test1