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Transition plan

The Data Handling System (DHS), providing the MARS and ECFS services, needs to be moved to Bologna before the new Atos HPCF will produce an increased archive load. A detailed migration timeline is shown in the transition plan below where all events are relative to day D, the day when the MARS and ECFS service will stop accessing the Main-DHS-Reading. Instead the MARS and ECFS service will be provided by a temporary DHS which has been pre-filled with essential data, necessary to continue operational and time-critical activities, with the aim to minimise the impact of the DHS move. After 6 days we will start filling the new Main-DHS-Blank with the data from the Temporary-DHS-prod and from the Main-DHS-Reading. At the end of the DHS-Move, expected to take 28 days, a new main DHS will become operational in Bologna. In preparation of the DHS move we will conduct a number of dry-runs during which the access to the main DHS in Reading will be blocked. The purpose of the dry runs is to verify that the Temporary-DHS does contain all essential data necessary to continue all critical activities during the move. Some of the dry-runs will last for 1-2 days. A final longer dry-run, lasting 5-7 days, is expected to happen 4 weeks before the move and will help to establish the exact date of day D.

Data Centre Migration to Bologna - User Space > DHS move - MARS and ECFS > transition_plan.PNG

Main service disruptions

The table below gives an indication of disruptions to the MARS and ECFS service foreseen as part of the DHS-Move.

Event	Date	Duration	Impact
Dry-run 1	September 2021, TBC	12 hours	degraded access to non-essential data
Dry-run 2	September 2021, TBC	24 hours	degraded access to non-essential data
...	...
Final dry-run	October 2021, TBC	5-7 days	degraded access to non-essential data
DHS-Move	November 2021, TBC	28 days	degraded access to non-essential data, with data becoming gradually available again during the move

Summary of impact by user group

User group	Impact
Member State User (fully registered computer user)	mars-client/WebAPI/ECFS - limited to essential data mars-client/WebAPI - No access to historical operational data and IFS research experiments mars-client/WebAPI - No access to public datasets (TIGGE/S2S, etc.)
Web User (registered by MS)	WebAPI - limited to essential data WebAPI - No access to historical operational data and IFS research experiments WebAPI - No access to public datasets (TIGGE/S2S, etc.)
Commercial and research user (maxch, comarc, resarc, nm)	WebAPI - No access to historical operational data and IFS research experiments WebAPI - No access to public datasets (TIGGE/S2S, etc.)
Public users	WebAPI - No access to public datasets (TIGGE/S2S, etc.)

Commercial users (comarc_*) with a valid licence during the outage will have the equivalent length of the outage added to their existing contract length.

Users may also opt to terminate their licence with 4 weeks notice.

Impact to MARS service

No impact expected

The following essential services/data are not expected to be impacted by the dry-runs and the DHS-Move:

Recent output (~ one month) from operational production systems: All products listed in the Catalogue of ECMWF real-time products, ERA5T (near real-time), CAMS, …
Observations, analysis input, tropical cyclones for the entire period
ERA5 data required as initial conditions for the operational hindcasts (20 years for the relevant weeks)
Archiving into MARS
MS Time-critical suites
Atos HPC testing

Access to non-essential services/data will be affected as described below.

Degradation of service/data access

Non-essential services and access to data degraded during dry-runs and the DHS-Move:

Retrieval via the WebAPI by MS-registered and commercial users will be limited to the essential data listed above
Retrieval via the MARS client on ECMWF computers will be limited to the essential data listed above

Unavailability of service/data

The following services/data will not be available during dry-runs and the DHS-Move:

Public datasets
ADS/CDS data served by MARS
IFS Research experiments
Historical operational data, non-essential ERA5 data

Impact to ECFS service

During dry-runs and the DHS move access to data archived in ECFS which has not been identified as essential will not be available. However, archiving into ECFS should not be affected by the DHS migration.

Recommended user action

Users of MARS and ECFS are urged to check if and how their work might be affected by the DHS-Move and plan accordingly.
Major changes to production processes etc. are best avoided during this period. For some activities the best course of action might be to avoid the migration period entirely...
Users missing access to data for any critical activity during the DHS-move should contact ServiceDesk at their earliest convenience with their requirements.