dCache Nearline Storage Driver for CTA

This is nearline storage plugin for dCache.

Building from source

Tar

To compile the plugin, run:

mvn package

This produces a tarball in the target directory containing the plugin.

RPM

mvn clean package
mkdir -p rpmbuild/{BUILD,RPMS,SOURCES,SPECS,SRPMS}
cp target/dcache-cta*.tar.gz rpmbuild/SOURCES
rpmbuild -ba --define "_topdir `pwd`/rpmbuild" target/SPECS/dcache-cta.spec

Using the plugin with dCache

To use this plugin with dCache, place the directory containing this file in /usr/local/share/dcache/plugins/ on a dCache pool. Restart the pool to load the plugin.

To verify that the plugin is loaded, navigate to the pool in the dCache admin shell and issue the command:

hsm show providers

The plugin should be listed as dcache-cta.

To activate the plugin, create an HSM instance using:

hsm create osm name dcache-cta [-key=value]...

example:

hsm create osm cta dcache-cta -cta-user=userA \
     -cta-group=groupA -cta-instance-name=instanceA \
     -cta-frontend-addr=cta-forntend-host1:17017,cta-forntend-host2:17017 \
     -cta-use-tls=true \
     -io-endpoint=a.b.c.d -io-port=1094

The dCache files stored in CTA will have hsm uri in form

<hsmType>://<hsmName>/<pnfsid>?arichiveid=<id>

Where id represents the CTA internal archiveId

for example:

osm://cta/00001D43C0C086CA459298C634D67F68AB6B?archiveid=8402

In the CTA catalog the dCache's pnfsids are referenced as disk_file_id field:

db => select * from archive_file where disk_file_id = '00001D43C0C086CA459298C634D67F68AB6B';
-[ RECORD 1 ]-------+-------------------------------------
archive_file_id     | 8402
disk_instance_name  | instanceA
disk_file_id        | 00001D43C0C086CA459298C634D67F68AB6B
disk_file_uid       | 1
disk_file_gid       | 1
size_in_bytes       | 10482
checksum_blob       | \x0a08080112043309f498
checksum_adler32    | 2566129971
storage_class_id    | 81
creation_time       | 1635150624
reconciliation_time | 1635150624
is_deleted          | 0
collocation_hint    |

NOTE: dCache-CTA driver doesn't preserve file's ownership, thus values of uid and gid fields contain arbitrary values.

dCache pool configuration

As CTA has its own scheduler and flush/restore queue the dCache pools should be configured to submit as much request as possible. Thus grouping and collecting request on the pool side should be disabled:

queue define class -expire=0 -pending=0 -total=0 -open <hsmType> *

The available configuration options:

Name	Description	required	default
cta-instance-name	The dCache instance name configured in CTA	yes	-
cta-frontend-addr	A comma separated list of CTA cta-dcache endpoints	yes	-
cta-user	The dCache instance associated user in CTA	yes	-
cta-group	The dCache instance associated group in CTA	yes	-
cta-ca-chain	The path to CA root chain for use with TLS	no	-
cta-use-tls	A switch (true/false) to enable TLS for CTA control connection	no	false
cta-frontend-timeout	How log dCache waits in seconds for CTA frontend to reply	no	30
io-endpoint	The hostname or IP offered by dCache for IO by CTA	no	hostname
io-port	The TCP port offered by dCache for IO by CTA	no	-
restore-success-on-close	obsolete	-	-

Load balancing and failover

If multiple cta-frontend-addr are provided, the driver will try to connect to all endpoints and use round-robin strategy to distribute the requests. If TLS is used, then all endpoints names should be present in SAN field of the certificate.

Compatibility with CTA

The driver is compatible with all dCache versions staring 7.2. The compatibility CTA versions are:

CTA Version	dcache-cta version
5.7.12 - 5.10.xx	0.6.0 - 0.14.0
5.11.0 - xxx	0.15.0

Acknowledgements

This driver is based and inspired by cta-communicator by Lea Morschel and sapphire by Svenja Meyer