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>?archiveid=<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	-
use-dio	Use Direct-I/O	no	false
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

External Contribution Formalities

Each externally submitted patch must have a "Signed-off-by" line. Patches without this line will not be accepted.

The sign-off is a simple line at the end of the explanation for the patch, which certifies that you wrote it or otherwise have the right to pass it on as an open-source patch. The rules are pretty simple: if you can certify the below:

    Developer's Certificate of Origin 1.1

    By making a contribution to this project, I certify that:

    (a) The contribution was created in whole or in part by me and I
         have the right to submit it under the open source license
         indicated in the file; or

    (b) The contribution is based upon previous work that, to the best
        of my knowledge, is covered under an appropriate open source
        license and I have the right under that license to submit that
        work with modifications, whether created in whole or in part
        by me, under the same open source license (unless I am
        permitted to submit under a different license), as indicated
        in the file; or

    (c) The contribution was provided directly to me by some other
        person who certified (a), (b) or (c) and I have not modified
        it.

    (d) I understand and agree that this project and the contribution
        are public and that a record of the contribution (including all
        personal information I submit with it, including my sign-off) is
        maintained indefinitely and may be redistributed consistent with
        this project or the open source license(s) involved.

then you just add a line saying ( git commit -s )

Signed-off-by: Random J Developer <random@developer.example.org>

using your real name (sorry, no pseudonyms or anonymous contributions.)

Acknowledgements

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