The setup:

Server 1 - SQL Server 2016 Enterprise - 13.0.6430.49 on Windows Server 2016 Datacenter

Server 2 - SQL Server 2019 Enterprise - 15.0.4280.7 on Windows Server 2019 Datacenter

Both servers are in Azure Both backup directly to storage account - URL

Backup is done with 64 stripes with these options:

,STATS = 10 
,BLOCKSIZE = 65536

I am in the process of migrating a 19TB database from Server 1 to Server 2.

Server 2 was built identically to Server 1, same SQL configurations etc.

The 19TB DB in question compressed backup size is 6TB.

On Server 1 (SQL 2016), the backup takes 5 hours and averages 700MB/sec

On Server 2 (SQL 2019), the backup takes 12 hours and averages 300MB/sec

I am using the exact same script to do the backup and it goes to the same storage account.

My observation: On Server 2, the backup runs at 700MB/sec for the first 2 hours and then at exactly 2 hours, it starts slowing down. The wait type recorded is ASYNC_IO_COMPLETION

Besides the version differences, the only other difference is that Server 2 is part of an AG so it's clustered.

Here is a snippet of what happens - Data Disk Read Bytes/Sec enter image description here

Are there any known issues with backup performance in SQL 2019?

Any ideas


  • What tier in Azure is the old server vs the new one?
    – J.D.
    Jun 11, 2023 at 16:51
  • They're both Standard E64-32s v3 Jun 11, 2023 at 19:39
  • Old server has 12 x P40 disks pooled to make a 24TB disk for data files. New server has 15 x P40 disks pooled to make a 30TB disk for data files. Both configured with 3 x column width Jun 11, 2023 at 19:41
  • 2
    Have you excluded subsystem issues by writing a 6TB file to both systems and comparing timings using IOMeter or CrystalDiskMark or similar? Jun 12, 2023 at 0:04
  • ^Seconded using CrystalDiskMark. It'll help rule out if the issue is internal to your SQL Server instance or not, pretty easily.
    – J.D.
    Jun 12, 2023 at 1:27


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