William Assaf diagnoses an issue:
If you’ve tried doing Backup to URL with SQL Server using a Shared Access Signature (SAS) certificate and received this error:
Error: 18204, Severity: 16, State: 1.BackupDiskFile::CreateMedia: Backup device ‘https://account.blob.core.windows.net/container/folder/msdb_log_202005170801.trn’ failed to create. Operating system error 50(The request is not supported.).Cannot open backup device ‘https://account.blob.core.windows.net/container/folder/msdb_log_202005170801.trn’. Operating system error 50(The request is not supported.). [SQLSTATE 42000] (Error 3201) BACKUP LOG is terminating abnormally. [SQLSTATE 42000] (Error 3013). NOTE: The step was retried the requested number of times (1) without succeeding. The step failed.
You may have received the same error I encountered.
This error popped up only after startup of SQL Server. To resolve the problem, we’d recreate the SAS key, using the same cert in the same script, and the backups would start working again. This affected all types of SQL database backups.
William did some troubleshooting and explains the core problem. It’s a weird one.