Veeam Agent for Windows 2.1 – Change Block Tracking Filter Driver (Part II)

Veeam Agent for Windows 2.1 – Change Block Tracking Filter Driver (Part I)

In my previous blog (link above), I introduced the new Change Block Tracking Filter driver that’s being shipped with the upcoming Veeam Agent for Windows 2.1. In this post I will share some performance testing that I have gone through (VAW / Veeam Volume CT Driver As you’ll see the increased performance and overall backup time is quite impressive!


Veeam Environment:Veeam Backup & Replication (All-in-One Veeam / Proxy / Repository E:Backup)Repository: ReFS 64K – 250GB

Managed Agent Node:Windows Server 2016 StandardC: – 40GBE: – 100GB NTFSE: was pre-populated with 30GB of random data.

Test 1 – No CBT Driver

Full Backup with No CBT Driver took 14:37 and the processing speed was around 250MB/s

After the full, I then added 60GB worth of change into the E: taking the overall used capacity from 30GB to approximately 90GB

Now we ran an incremental backup. So, without an actual change block tracking driver Veeam Agent must scan the Windows master file table (MFT) to read the metadata and identify individual files that have changed. Notice in the image below that (1) illustrates the total 90.1GB worth of data that’s been read HOWEVER the data transferred (2) is 60.5GB. This recognizes that the only data that’s been changed is the 60.5GB but we had to read the entire 90.1GB had to be read to determine the changes. Lastly, this incremental took 13:01 (3).

Test 2 – With CBT Driver

For this test I returned the environment back to the same state as where we began above by deleting the 60GB worth of changed data, leaving only the original 30GB that was present on E:.

Full Backup with CBT Driver took 10:57 and the processing speed was 3GB/s! The full backup is much faster as Veeam Agent no longer needs to calculate digests.

After the full, just like above, E: was populated with the same 60GB worth of change taking the overall used capacity from 30GB to approximately 90GB.

Now for the wow!

I next ran an incremental backup. It’s worth noting that Veeam CTStore is located at C:Program DataVeeamEndpoint DataCTStore (more details on the .vct files in the next post).

With the CBT Driver Veeam will grab the block map from the CTStore and compare with the backup and begin the backup process. Examining the MFT is no longer required. The illustration below (1) shows the 60GB worth of data added is the amount of data read – unlike in the example above where the read data was 90.1GB – proving that Veeam is locating only the changed blocks and not examining files which results in a MUCH faster incremental backup (3) at 8:44 as compared to the 13:01 before and the overall processing was doubled – from 247MB/s to 460MB/s. These are huge improvements that will positively benefit your applications and the overall backup window!


Veeam Agent for Windows 2.1 is introducing a way to backup your physical or cloud-based Windows Servers in a faster and more efficient manner making it an absolute must for highly transactional workloads like SQL, Exchange or File Server. You’ll want to keep your eye on for the latest updates and notifications of when this awesomeness becomes generally available.

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