Bandwidth needs for SAN to SAN (Site to Site) replication
I'm looking at replicating 2 SANs across the WAN, site to site. I would want the replication to be as real time as possible < 15 min difference. From my calculations, my current SAN is getting an average of 1.25 megabytes per second written to it. So what I need to know is the type of connection and speed I would be looking at to achieve this. There would be nothing else on this link, just the SAN replication traffic. If I figured full speed achievement of data connections I think I would be looking at at least 10 MBit (8mbit connection = approx 1mbyte per second), but I'm not sure that would be enough to calculate for the overhead.
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2 Dell Equllogic SAN's, for the sake of this article I want to think of no compression.
if you have an average of 1.25mB/s then what does it spike to ? How long would it take to "recover" from the spike ?
How much data are you replicating ?
If you already have both on-site, then I would setup replication via a managed switch and monitor bandwidth usage, ideally with sflow/netflow, but SNMP would do at a pinch, or setup a monitor/span port and use ntop
You might want to look at the cost of a 1000mb line against the cost of a Riverbed or similar to do block based "compression".
If the link is in the same city, then it's probably a lower cost option to go for the bandwidth, if its between cities, then a Riverbed or similar might be a better option.
How much data are you replicating ?
If you already have both on-site, then I would setup replication via a managed switch and monitor bandwidth usage, ideally with sflow/netflow, but SNMP would do at a pinch, or setup a monitor/span port and use ntop
You might want to look at the cost of a 1000mb line against the cost of a Riverbed or similar to do block based "compression".
If the link is in the same city, then it's probably a lower cost option to go for the bandwidth, if its between cities, then a Riverbed or similar might be a better option.
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I would usually suggest that the initial sync (especially on small arrays) is done locally.
By small I mean low tens of TB.
By small I mean low tens of TB.
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The way I figured the average data usage, was to take the write data on the SAN listed by each iscsi connection from the Xen server, and divide the total data used by the number of hours connected, and then add those together to get the total per hour write data. (See Attached). I do see an issue with this as it doesnt give me the peak.
I know the built in Equallogic SAN replication does it's own compression, but not sure what it actually amounts to.
Looking at the Riverbed device I could definitely see an added benefit of adding it in the mix.
The end result here would be to replicate my Xen Storage pools in a colo, so that I could fail over with out losing too much data. It wouldn't necessarily have to be real time fail over, but I would at least like to be able to fail over to the remote site in the event of a disaster in under an hour, 30 minutes would be ideal.
The initial amount of data will be approx 4 TB
I know the built in Equallogic SAN replication does it's own compression, but not sure what it actually amounts to.
Looking at the Riverbed device I could definitely see an added benefit of adding it in the mix.
The end result here would be to replicate my Xen Storage pools in a colo, so that I could fail over with out losing too much data. It wouldn't necessarily have to be real time fail over, but I would at least like to be able to fail over to the remote site in the event of a disaster in under an hour, 30 minutes would be ideal.
The initial amount of data will be approx 4 TB
What will you have running in the guests ?
Although SAN replication can be good, usually this would be sync rather than async which you are planning.
You also need to have a process of failing back, and preventing the main site guest from starting up or replicating while the remote site guest is running.
I would tend to look at moving towards HA rather than DR, this then gives you the capability of switching over to the remote site for maintenance etc with minimal downtime. For you to do a clean move using snapshot based replication, you would need to shut down the guest, then wait for replication to complete and then start up the guest on the remote, so your 15 minute replication time could be considerably longer.
Although SAN replication can be good, usually this would be sync rather than async which you are planning.
You also need to have a process of failing back, and preventing the main site guest from starting up or replicating while the remote site guest is running.
I would tend to look at moving towards HA rather than DR, this then gives you the capability of switching over to the remote site for maintenance etc with minimal downtime. For you to do a clean move using snapshot based replication, you would need to shut down the guest, then wait for replication to complete and then start up the guest on the remote, so your 15 minute replication time could be considerably longer.
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Inside the guest is the usual, a couple of DC's (with failover DNS, 2ndary DHCP scopes, etc), Exchange 2007, Sql 2008, a file server, ts, SharePoint Moss, and a couple of application server, that host some applications that have the sql server as their back end. All are Server 2008 (most are Enterprise).
I would be open to just looking at a secondary HA site rather than failover, in fact if I can get the log shipping, etc, down for exchange and sql it would be preferred for those things like you state as maintenance, etc.
That being said I would still need to figure out the bandwidth type and requirements to keep up with that.
I would be open to just looking at a secondary HA site rather than failover, in fact if I can get the log shipping, etc, down for exchange and sql it would be preferred for those things like you state as maintenance, etc.
That being said I would still need to figure out the bandwidth type and requirements to keep up with that.
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I can spec the servers (ex, SQL, FS, etc) out if needed. i.e. size, db's, etc.
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Is there any overhead from it ? or compression ?
what type of data is on the SAN ? would replication be better done at the application layer e.g. Exchange 2010 DAG instead of doing block level SAN replication ?