Missing rows in Azure SQL after using DMS to migrate MS SQL from VM

Question

Missing rows in Azure SQL after using DMS to migrate MS SQL from VM

Kamil Kwiaton 1

We were migrating MS SQL database from Azure Virtual Machine into Azure SQL. We use Microsoft Service to do that (Database Migration Service).

Whole migration completed successfully but we noticed that in one table we have over 3 milion missed rows.

Table before migration:

User's image

Table after migration to Azure SQL:

User's image

DMS is returning success status for that table:

User's image

Like it didn't read some rows. Rows which was not migrated are not any different then others except that it have NULL on one column. Every row which had a NULL on specific field are not migrated for that one table. Other columns with NULL work fine.

Of course the column is properly set to allow null values:

User's image

Is this some issue or limitation which we triggered? When i manually change the value on target DB it works and allow me to do that.

Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-18T17:19:51.5833333+00:00

Hi Kamil Kwiaton

I kindly request you to please share the details requested in the private message for further troubleshooting.
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-21T17:07:54.81+00:00

Hi Kamil Kwiaton

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Kamil Kwiaton 1 Reputation point

2025-07-21T18:30:09.0733333+00:00

Yes, i responded in private message. Thanks.
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-22T16:07:53.38+00:00

Hi Kamil Kwiaton,

Can you please check if there is table with name

dbo.__migration_status in the target Azure SQL , if it is there can you please share the data where column STEP = 31 .

This table is created by DMS to monitor the migration
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-23T16:48:46.4366667+00:00

Hi Kamil Kwiaton

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-24T16:43:07.5333333+00:00

Hi Kamil Kwiaton,

Thanks for sharing the details. Our internal team is actively investigating the root cause to ensure this doesn't happen again. I will get back to you soon with an update.
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-26T00:28:25.5233333+00:00

Hi Kamil Kwiaton,

Could you please try the workaround and the let us know the result.
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-29T18:47:15.6233333+00:00

Hi Kamil Kwiaton,

Just checking in to see if the below answer helped. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

1 answer

Your answer

Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-18T17:19:51.5833333+00:00

Hi Kamil Kwiaton

I kindly request you to please share the details requested in the private message for further troubleshooting.
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-21T17:07:54.81+00:00

Hi Kamil Kwiaton

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Kamil Kwiaton 1 Reputation point

2025-07-21T18:30:09.0733333+00:00

Yes, i responded in private message. Thanks.
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-22T16:07:53.38+00:00

Hi Kamil Kwiaton,

Can you please check if there is table with name

dbo.__migration_status in the target Azure SQL , if it is there can you please share the data where column STEP = 31 .

This table is created by DMS to monitor the migration
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-23T16:48:46.4366667+00:00

Hi Kamil Kwiaton

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-24T16:43:07.5333333+00:00

Hi Kamil Kwiaton,

Thanks for sharing the details. Our internal team is actively investigating the root cause to ensure this doesn't happen again. I will get back to you soon with an update.
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-26T00:28:25.5233333+00:00

Hi Kamil Kwiaton,

Could you please try the workaround and the let us know the result.
Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-29T18:47:15.6233333+00:00

Hi Kamil Kwiaton,

Just checking in to see if the below answer helped. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Answer 1

Mahesh Kurva 7,090 Microsoft External Staff Moderator

Hi Kamil Kwiaton,

As per out analysis the issue is because of used_parallel_copies = 4 . As a workaround try using just 1 node for migration instead of using 4 nodes and retry the migration for that particular table.

Hope this helps. Do let us know if you any further queries.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Mahesh Kurva 7,090 Reputation points Microsoft External Staff Moderator

2025-07-30T15:41:17.5233333+00:00

Hi Kamil Kwiaton,

Following up to see if the above answer helped. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

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Missing rows in Azure SQL after using DMS to migrate MS SQL from VM

1 answer

Your answer