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bfleisch
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Replicate a replica ?

Post by bfleisch »

Hello Veeam users!

Does anyone know whether replicating a replica is a supported feature ? (or that is has been tested ?)

I would like to setup a replication job between 2 ESX hosts in my main site, and have a second replication job to a DR site. What would be the most effective way to do this ?

* Replicate the replicas ?
* Replicate twice the VMs (one time on the main site, second time on the DR Site ) ? The main issue I see here is that I can not run these jobs in the same time, as the VM is snapshotted during the replication process...

What are you views on this ?

Many thanks for your feedback,

Best regards,

Bruno

Gostev
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Re: Replicate a replica ?

Post by Gostev » 1 person likes this post

Hello, I do not see any issues with replicating a replica VM. Replicating from source VM might provide more reliability though, as you will replicate actual source data, versus replicating a copy of source data which already undergone some processing. Obviously the drawback is more stress on source (production VM) due to additional snapshot operations.

To avoid conflicts, you just need to schedule the jobs in a way so that they run in different times - I see no problems here.

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Re: Replicate a replica ?

Post by bfleisch »

Hi Gostev,

Thanks for the fast answer -

Best regards,

Bruno

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Re: Replicate a replica ?

Post by Gostev »

Just wanted to update the thread with one issue I have determined for this scenario later. You will not be able to use ESX4 changed block tracking for the second job, as only guest initiated I/O is tracked by ESX4 changed block tracking, while in this scenario, "source" VMDK for the 2nd replication job will be modified by external application (1st replication job). You will however be able to use legacy change tracking mechanism that Veeam Backup implements, it is just not as fast. To do this, simply disable the use of ESX4 changed block tracking in the Advanced replication job settings (on vSphere tab).

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Re: Replicate a replica ?

Post by JoeH »

I'm currently investigating a dual-replication scenario as well. However, my DR replica is located across a relatively slow WAN link, so I need to minimize the amount of data transferred...I'm also using ESXi V4, so I cannot utilize data compression.

Obviously, I'll need to seed the DR replica, a mechanism Veeam kindly provides. So now I look at the same methods as Bruno:
1) Replicate the local replica?
2) Replicate the source host twice?

My first thought was to use #2, as I believe that I need Changed Block Tracking to get the data to the DR site in a decent timeframe (by minimizing the amount of data that must cross the WAN).

However, Anton brings up the possibility of disabling ESX4 Changed Block Tracking, and using the legacy change tracking mechanism within Veeam Backup. This would minimize the load on my source host - I'd only have to snapshot it once instead of twice.

So, I guess I'd like to get a feel for a couple of things:
- How much impact does the additional replication snapshot have on the source host?
- How can I measure this impact?
- How much slower is the legacy Veeam change tracking mechanism than VMWare Changed Block Tracking?

Last - assuming that I replicate the source host twice - is there any issue with the Changed Block Tracking data? Does having 2 replication jobs going against the same source host cause any problems with maintaining which set of Changed Block data is associated with which replication job?

Thanks - I appreciate your time!
-Joe

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Re: Replicate a replica ?

Post by Gostev »

With vSphere, you should definitely go with option 2, no doubt. Due to the use of changed block tracking, the load produced by the incremental job runs are minimal. Our customers have reported that after update to vSphere and Veeam v4 they often started to trigger jobs during business hours when required for some servers - and there is no noticeable effect on production due to only changed blocks being processed.

Legacy Veeam change tracking mechanism is about 10x slower, and puts 10x more load on your environment as it requires to read the whole VM disk image to be able to determine changes since last pass.

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Re: Replicate a replica ?

Post by JoeH »

Anton, thanks for the detailed information!

I really appreciate all the time and energy you (and the others on the Veeam team) put into these forums!

Thanks- Joe

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Re: Replicate a replica ?

Post by EddyChong »

Gostev wrote:Just wanted to update the thread with one issue I have determined for this scenario later. You will not be able to use ESX4 changed block tracking for the second job, as only guest initiated I/O is tracked by ESX4 changed block tracking, while in this scenario, "source" VMDK for the 2nd replication job will be modified by external application (1st replication job). You will however be able to use legacy change tracking mechanism that Veeam Backup implements, it is just not as fast. To do this, simply disable the use of ESX4 changed block tracking in the Advanced replication job settings (on vSphere tab).
Hi I've also come across the replicating a replica question lately. My situation is i replicated from production to my DR, and from my DR i would like to replicate the replica to another host which is in the same site.

The vSphere version is 5.1 and Veeam v7

My concern is the 2nd replication mentioned by Gostev which changed back tracking is not available for the 2nd replication problem is still present in vSphere 5.1?

Thanks
Eddy

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Re: Replicate a replica ?

Post by foggy »

Eddy, this is not specific to vSphere version. Please see another related thread: Backup the replicated VMs.

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Re: Replicate a replica ?

Post by EddyChong »

Hi Foggy,

Thanks! This cleared my questions!

Thanks
Eddy

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Re: Replicate a replica ?

Post by Gostev »

This is certainly not specific to vSphere version, but rather specific to B&R version. Starting B&R 6.0, we create replica restore points differently (through ESXi, without applying external modifications to VMDK), thus all changes should be tracked properly. Thus, I am not quite sure if my quote above (from 3 years ago) still applies. Foggy, can you please test this with v7 and update us?

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Re: Replicate a replica ?

Post by foggy »

In fact, the topic I've referred to above provides more detailed and actual info (as of v6): regardless of the CBT setting in the job, our proprietary change tracking mechanism will be used. I guess it's the same for v7, but I'll check.

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Re: Replicate a replica ?

Post by unixbloke »

A few years on .. I'm running V10 and wishing to do a similar task. I run local replication of an MSSQL database hourly and it takes about 5mins to run, I need to replicate to a remote site but the link is slow and therefore a second Replica of the primary source can take 45 mins to run! What's the recommended approach?

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Re: Replicate a replica ?

Post by Vitaliy S. »

Not sure there is a fix for the low bandwidth issue, but this thread talks about replicating a VM replica and not the source one. Based on what I see in your post, you have created a secondary replication job to replicate your source VM to another site and it takes more time than you expected, right?

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Re: Replicate a replica ?

Post by foggy »

Hi Mike, if the slow link is the major concern, consider using WAN acceleration available within the replication job.

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Re: Replicate a replica ?

Post by unixbloke »

Vitaliy, I created the 2nd Replication job to see how quick/slow the job would run, it was still running 12 hrs after I started it this morning so I've binned that Idea! But my objective is having a replica on a second site by what ever means. So it looks like I'll try using the 1st replica as a source.

Foggy, I'll look at WAN accelleration as well.

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Re: Replicate a replica ?

Post by Vitaliy S. » 1 person likes this post

Using the 1st replica as a source should not change anything significantly, as the main bottleneck is the WAN link.

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Re: Replicate a replica ?

Post by foggy » 1 person likes this post

It can even make things worse as CBT cannot be used when backing up/replicating a replica.

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Re: Replicate a replica ?

Post by unixbloke »

I'm just deploying a couple of WAN Accelerators .. I'll update the thread with my finding.

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Re: Replicate a replica ?

Post by unixbloke »

So quick update .. I've deployed two WAN Accelerators, one on each site. Initial replication took 14hrs which meant my local 1 hourly replication had to be disabled during that period. I had hoped once the initial replication had finished subsequent replications would take a similar time to the hourly job ie 5-10mins but alas no. The second remote replication had to be aborted after 1hr 30min having completed only 10% of the replication.

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Re: Replicate a replica ?

Post by foggy »

What was selected as the replica source in this case? That shouldn't be the case since only increments are transferred during subsequent runs. Have you compared the amount of transferred data by the moment you aborted the job with that of the first job run during a similar amount of time? What was reported as the major bottleneck for the WAN job?

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Re: Replicate a replica ?

Post by Vitaliy S. »

In addition to what has foggy asked, can you re-confirm that you were replicating a replica and the source VM? If that's the case, then replicating a replica will not bring you a required boost, since CBT data cannot be used in that case.

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Re: Replicate a replica ?

Post by unixbloke »

For this test I am replicating the Source VM. The job is saying that the Source VM is the bottleneck (Load: Source 57% > Source WAN 10% > Network 6% > Target WAN 0% > Target 18%) it transferred 720MB in the 90mins whereas the initial replication transferred 200gb in the 14hrs. I'll raise a support call so you guys can look at the logs and setup properly.

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Re: Replicate a replica ?

Post by Vitaliy S. »

Since source is the bottleneck, I would also suggest looking at how you retrieve data from the production storage. Playing with the source data retrieval mode can help with optimizing job performance.

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