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evilaedmin
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Restoring to thin or EagerZeroedThick disks

Post by evilaedmin » Sep 27, 2018 9:11 pm

The direct SAN restore guide hints at the performance differences between restoring to a Thin disk vs. EagerZeroedThick:
https://helpcenter.veeam.com/docs/backu ... tml?ver=95
As a result, restore of thin disks involves extra allocation overhead if compared to restore of thick disks, which results in decreased performance.
In our environment with Dell SC (Compellent) 7.2, using the thin disk option is almost anywhere between 10-20x slower than EagerZeroedThick. For smaller machines, restoring as EagerZeroedThick is not such a big deal because Dell SC does not write zeroes to back end and the accelerated creation operation is fast, but for larger machines creating the EagerZeroedThick disk itself takes hours before any data begins restoring -- which makes on wonder if the accelerated creation operation is functioning correctly.

Is everyone is experiencing a difference of such magnitude between the two disk formats when doing a full restore? When restoring to thin, the proxy which is restoring the data via hotAdd experiences virtual disk latencies greater than 200ms.

DavoudTeimouri
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Re: Restoring to thin or EagerZeroedThick disks

Post by DavoudTeimouri » Oct 25, 2018 6:51 am

I think, you can restore the VM as thin and then convert disk type to EagerZeroed by storage migration.
It can be done durin non-working hours.
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evilaedmin
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Re: Restoring to thin or EagerZeroedThick disks

Post by evilaedmin » Oct 25, 2018 2:47 pm

Hi DavoudTeimouri:

Yes, that is possible, but not practical in a reasonable amount of time either. When the proxy VM is writing out data in Thin format, it experiences in our environment extreme latencies (250ms per io) leading to extremely poor restore throughput. Thus part of my question is if this is unique to our configuration or if others have experienced this.

DavoudTeimouri
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Re: Restoring to thin or EagerZeroedThick disks

Post by DavoudTeimouri » Oct 26, 2018 7:03 am

Hi,
What about LazyZeroed? Also if you have high latency, you have big problem with storage array and using thin or thick is not different to you.
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evilaedmin
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Re: Restoring to thin or EagerZeroedThick disks

Post by evilaedmin » Oct 26, 2018 7:45 pm

DavoudTeimouri wrote:
Oct 26, 2018 7:03 am
What about LazyZeroed?
LazyZeroed behaves the same as thin.
DavoudTeimouri wrote:
Oct 26, 2018 7:03 am
Also if you have high latency, you have big problem with storage array and using thin or thick is not different to you.
latency of 250ms when using thin or lazyZeroed, 5ms when using EagerZeroedThick.

foggy
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Re: Restoring to thin or EagerZeroedThick disks

Post by foggy » Nov 15, 2018 5:14 pm

I wouldn't say this is unique to your configuration, since initially there was no eager zeroed disks restore mode in Veeam B&R (probably due to the behavior you see for large disks, when disk preallocation takes quite long). Several versions ago we implemented it based on customers' requests.

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