NtfsDisableLastAccessUpdate to reduce CBT?

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NtfsDisableLastAccessUpdate to reduce CBT?

Veeam Logoby mplep » Mon Oct 25, 2010 9:08 pm

Hi,

I'm looking at ways to reduce the amount of CBT on my Windows VM's. I've found a lot of discussions on the web regarding SAN snapshots and the NtfsDisableLastAccessUpdate registry value in Windows. I've also found a couple of posts on these forums as well. The general recommendation was to disable this feature as it can otherwise mark lots of blocks as changed even though they have just been opened and not actually modified.

Does anybody have knowledge or experience of this and whether is makes a difference?

Thanks

Mark
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Re: NtfsDisableLastAccessUpdate to reduce CBT?

Veeam Logoby mplep » Tue Oct 26, 2010 4:31 am

Hi,

I just wanted to share an interesting result. I had a couple of VM's which were taking about 6hrs to incremental sync across a 100MB line which was not far off full sync times! I found that both these servers (Database/Exchange) had daily backups performed to local volumes. I moved these backups to dedicated volumes which I then excluded from Veeam. The result is both servers are down to about 35mins sync time now and have deltas about 1/5 the original size.

It seems obvious in hindsight, but as I didn't manage these SQL/Exchange backups I wasn't aware of their "backup folders" presence upon local volumes initially.

I don't have any results for disabling NtfsDisableLastAccessUpdate yet though.

Mark
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Re: NtfsDisableLastAccessUpdate to reduce CBT?

Veeam Logoby folerx » Mon Sep 19, 2016 6:54 am

Any update on this?
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Re: NtfsDisableLastAccessUpdate to reduce CBT?

Veeam Logoby Mike Resseler » Mon Sep 19, 2016 8:15 am

Daniel,

Can you clarify. These previous posts are a few years old. Just for your information, there is no need to use this registry value. When we protect VMs, we are looking at block level changes and a last access update doesn't make the block change... Is this what you asked for?

Thanks

Mike
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Re: NtfsDisableLastAccessUpdate to reduce CBT?

Veeam Logoby folerx » Mon Sep 19, 2016 8:16 am

Yes, tnx
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Re: NtfsDisableLastAccessUpdate to reduce CBT?

Veeam Logoby dellock6 » Mon Sep 19, 2016 4:40 pm

Well, actually "any" change at the vm level is a write IO that updates the underlying block, so there is a change. However, I agree those posts are 6 years old, so Daniel if you need any additional informatio, you'd better post here your use case so we may help.
Luca Dell'Oca
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Re: NtfsDisableLastAccessUpdate to reduce CBT?

Veeam Logoby Mike Resseler » Mon Sep 19, 2016 5:24 pm

Yes, as Luca says, a bit more information is needed. For example, starting from Vista (and I believe from 2008 R2) this registry is there by default and won't update it anymore.
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