DISKSPD benchmarks disk I/O performance through the command line. It simulates different I/O patterns, measures latency, and assesses storage subsystem performance. By customizing parameters like block size, I/O depth, and threads, you can create synthetic workloads that mimic real-world scenarios and help identify potential bottlenecks. In this artcile, we shall discuss “Veeam Backup and Replication Disk I/O with diskspd”. Please, see Fixing AIX Veeam agent job startup delay issue, and Set up Veeam Backup for Microsoft Azure.

Recently, I ran into an issue where AIX backup jobs were taking longer than expected to start. After digging around, I came across a very useful Veeam KB article (KB2014) that suggests testing disk I/O to identify potential bottlenecks, especially useful when backing up to tape or dealing with performance inconsistencies.

I decided to try out one of popular tools for benchmarking and simulating disk workloads: DiskSpd (for Windows).

Step 1 – Install Disk Benchmark Tool

Make sure you have the following installed:

diskspd– Microsoft’s free disk performance tool for Windows.

Step 2 – Run DiskSpd on Windows

Here’s the command I used:

diskspd.exe -c25G -b512K -w100 -Sh -d600 D:\testfile.dat

Explanation of parameters:

-c25G → Size of the test file (25 GB). This should reflect the typical size of your restore points.
-b512k → Block size of I/O operations.
-w100 → 100% write test (you can adjust for read/write mix if needed).
-Sh → Disables hardware and software caching for accurate results.
-d600 → Test duration (600 seconds = 10 minutes).

Note: Using a test file that’s too small can result in artificially fast results due to caching.

And here’s what I got back from the test:

Summary:

Total Data Written: ~384.7 GB
Write Throughput: 656.57 MiB/s (~688 MB/s)
IOPS: 1313.13
No read operations, as expected with -w100

This is a very solid performance result. Sustaining over 650 MiB/s in sequential write means the disk subsystem is not a bottleneck in my scenario with AIX.

Also, you can run the same test at the AIX side, but using fio tool.

Please, see Upgrade VBR to 12.3.1: Setup detected inconsistent configuration, how to In-place upgrade of Windows Server 2022 to 2025 and how to Export and Convert Private Keys to .PEM Format in Windows.

Takeaways

Always benchmark your backup repository if you’re experiencing slow tape performance or synthetic operations.
Check disk health, defragmentation, caching, and filesystem-level issues.
The diskspd tool is lightweight and can be easily included in your troubleshooting process.
This test complements what Veeam does behind the scenes with synthetic I/O.

I hope you found this article very useful on “Veeam Backup and Replication Disk I/O with diskspd”. Please, feel free to leave a comment below.