Question on Continuous replication

[gcballard]

We don't really use the replication feature much as we are replicating via SAN, but I thought that I could use the Veeam replication to protect my vcenter server. I was originally headed down the road of SQL replication but had issues and thought that Veeam would be a lot easier. It turns out it was but I had some issues that I'd like the community's input on.

The vcenter server is on a stand-alone host and running as a VM. SQL is on this box as well. I set up continuous replication to one of our hosts and a Datastore running our production environment (Cisco UCS and Compellent SAN). After a period of time (an hour?) I noticed that a disk latency alert had triggered on a bunch of VMs. Well, our storage is Compellent so that storage is virtualized so I figured that it was related. I stopped the replication and started looking at stats. Write latency on the LUN I was replicating to went through the roof while it was replicating. The amount of data being written was small so I was thinking it was due to SCSI LUN locking. But I started looking at other LUNs and noticed that some had identical spikes. I'm assuming this is related to the shared storage Compellent model. But if that's the case the latency shouldn't be due to LUN locking should it? I just want to understand this behavior better. Any comments are welcome.

vsphere 4.1u1
Veeam 6 p3
vCenter 5

[Gostev]

Does your Compellent firmware support VAAI?

[gcballard]

No. We have to get version 6 (of the firmware) for that. I'm not even sure if it's released yet.

[Gostev]

OK. Generally, I would not recommend continuous replication with non-VAAI enabled array because of performance hit from SCSI reservations (even if you find the cause of your issue to be different).

[gcballard]

Ok, that's really good to know. I still wish I understood why a little better but I think the SCSI reservations must have something to do w/ it. Thanks for your help Gostev.

[Gostev]

Check out this (very old) whitepaper from VMware on performance impact from SCSI reservations > Scalable Storage Performance (see page 6)

[gcballard]

thanks for the whitepaper Anton. I will educate myself further.

[kamalkant]

I have a question: Not sure if this the right page to ask this. But I am in need to set up continuous replication using Veeam with 30 Minutes restore Points. How should I go ?

Veeam replication Job does not give me an option to have the interval option and continuous option both.

[Gostev]

Based on your requirements, it sounds like you want to use "Periodically every" option on the Schedule page of the wizard, and pick 30 minutes as value. This will give you a restore point every 30 minutes. This is a pretty common schedule among Veeam replication users.

Continuous option will generate a restore point every few minutes, you don't want that. This will give you less than an hour worth of restore points, and too much stress on the production environment.