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SAN replication using all the bandwidth

Posted on 2009-07-15
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Last Modified: 2013-11-14
We have recently been having problems with bandwidth on a 1GB lan extension link between our office  and data centre.
The bandwidth used to average at about 2% - 10% but now averages at 35%+ with periodic bursts of over 100%.
 This is due to a new SAN that has been installed by an external company. They say that the SAN is permanently replicating and it is normal to use that amount of bandwidth.
 It is set to use up to 75% of available  bandwidth and that 35% is quite low.
Can someone confirm this is correct or even suggest a  solution other than get another link?
The links at the sites are 1gb into MDS switches.
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Question by:andrewsmith950
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Handy Holder earned 525 total points
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Site to site SAN replication can take a lot of bandwidth, for example if you use VMware and replicate the actual VMs and one is paging all that pagefile activity is unnecessarily replicated to the other site.
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by:giltjr
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The amount of bandwidth should be based on how much data you are writting to your SAN.

If  you are writing/updating a lot of data, then you will use a lot of bandwidth.

Based on your numbers (1 Gbps link with 35% utilization) that means you are doing about 300 Mbps which is about 37 MB per second.

If you were averaging 2-10% that means that you may have been doing 1-2MB per second before so the SAN replication added 35 MB per second.  What is your I/O rate to the local SAN.
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by:andrewsmith950
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1 gig
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by:giltjr
ID: 24869325
Are you saying you are updating 1 GB ps of data on your local SAN?

Or are you saying that the available bandwidth to your local SAN is only 1 Gbps?

What you need to look at is how much data per second do you update on your local SAN and then what you are replicating.  

As andyalder pointed out, there are somethings you should not be replicating, but you need to figure that out.

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by:andrewsmith950
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Thanks . I don't know a lot about SANs so was just confirming what I was being told. Many thanks
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by:giltjr
ID: 24872022
Thanks.  

Just a little F.Y.I.  SAN are really nothing more than disk drives attached via a network.  Instead of Ethernet and IP as their lower level networking protocols they typically use Fiber Channel and have their own private physical network.  They also typically have much more bandwidth than LAN, which is what you typiclaly think of when here networking.
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