Minimum acceptable WAN bandwidth for replication

[stevewalker]

Hi All,

I'm trying to plan for a site to site replication project that will require maybe once a day replication for a handful of VMs. We will have 2 x ESXi (licensed) 4.0 U1 hosts in the main site and 1 x ESXi (licensed) 4.01 U1 host in the DR site, connected by a 50Mbit directional wireless link between buildings (latency ~5ms).

Day 1, replication will be achieved when the two host servers are connected to the same LAN - we will configure backup and replication in situ before moving one of the hosts to the DR site. We are not envisaging particularly high turnover in data, we have a small domain controller, a couple of Citrix XenApp boxes, and a file server ~50GB with a small SQL database hosting the Citrix and Virtual Centre DBs.

Day 2+, we'll be relying upon using Veeam to make backups of the VMs direct to a local iSCSI SAN target that the two primary hosts are connected to and replicating each VM over the wire (once every 24 hours) to the DR site.

My question, first off - the Veeam documentation says we should have 1Gbit/s 'for performance' reasons. What kind of links are other people using? I don't want to over promise, but after all i'm not talking about providing CDP here, just a reliable off site backup of certain important VMs.

Secondly, if we're using an iSCSI SAN at both ends would it be better to set the replication target to be an iSCSI virtual disk that is connected to the Veeam B&R server or should I point it at the ESXi server itself for the best/most consistent performance?

If anyone has any suggestions they will be most appreciated!

Thanks - Steve

[Gostev]

Hello Steve, basically people use anything between 1Mb and 1Gb - this only depends on the total amount of daily changes in those VMs. I suggest that you try to replicate locally with your planned replication frequency, and observe/sum up the size of VRB files generated after each pass for each VM, and from that estimate the daily traffic and so the bandwidth requirements.

You can lookup some actual statistics from our customers in recent threads about different WAN accelerators, incidentally this has been a hot topic lately.

[stevewalker]

Awesome, thanks for giving me the figures. I guess it would be helpful somewhere if you could give some guidelines, maybe in the form of a table to show what the maximum amount of data might be for any given network bandwidth. Maybe i'll try that myself when I get testing perhaps.

On the question above of whether it's best to set the target for the replica a directly connected iSCSI volume on the B&R server (over the WAN) or to point it at the remote ESXi server - is there any preference?

[Gostev]

You can only target replicas to ESX or ESXi hosts, not volumes.

[jeremystw]

I found this tool helpful to calculate transfer times. It may be a bit optimistic considering it does not include latency, congestion, etc but it will at least give you a best case estimate.
http://www.calctool.org/CALC/prof/compu ... nsfer_time