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Fibre Channel uplinks - how many and how much?

 
wonderboy
Occasional Advisor

Fibre Channel uplinks - how many and how much?

I hope this will be a simple set of questions: 1. how many Fibre Channel uplinks do most people actually use? 2. are these uplinks split across redundant FC modules? 3. what percentage of the FC capacity is really utilized? I'm looking for real-world examples, not best practices from a white paper. [Updated on 2/11/2009 4:19 PM]
7 REPLIES
Neal Bowman
Respected Contributor

Fibre Channel uplinks - how many and how much?

For our ESX environment, we have 16 BL460c installed in each c7000, and we have both VC-FC modules fully linked (8 cables). These are going to redundant SAN fabrics. At this time, I do not know what our utilization of these links are.
wonderboy
Occasional Advisor

Fibre Channel uplinks - how many and how much?

To how many fabrics are you connecting? 8 uplinks full-up sounds like you've got a lot of SAN to deal with.
Neal Bowman
Respected Contributor

Fibre Channel uplinks - how many and how much?

we are connecting to 2 fabrics for redundancy. ESX only uses 1 link at a time, and from my understanding, will switch on demand. we are trying to limit our LUN sizes to 500G or less, and limit the number of devices that connect to these LUNs. We have seen lots of disk contention when we had larger LUN sizes.
wonderboy
Occasional Advisor

Fibre Channel uplinks - how many and how much?

Great information! Will you help me understand why you're using 8 uplinks to 2 fabrics? Are your VMs using that much capacity? Is over-subscription a concern? Is this just force of habit? (tongue in cheek)
Neal Bowman
Respected Contributor

Fibre Channel uplinks - how many and how much?

yeah, we are running 45 ESX hosts across these three chassis. Between these hosts, we have 5 ESX clusters of 9 hosts each to handle different classification of services. two of these clusters are dedicated for for VDI workstations, We're hosting over 800 XP workstations and over 300 Server 2003 VMs, and looking to add more. Our workstations typically have a 10G OS disk assigned, and a few have larger based on their needs/requirements. Our servers have a base of 20G and then any other partitions as needed. Our biggest issues we are seeing is memory oversubscription with the number of guests we are running. Our storage team assures us we are not pushing the SAN, except when 300+ XP machines reboot at the same time because of WSUS updates. that's what has forced us to go back and use more/smaller LUNs.
amemushaj
Occasional Visitor

Fibre Channel uplinks - how many and how much?

Doesn't the VC-FC simply distribute (vs link aggregation) the server links to the uplinks, ie: 16 blade's w/ 4 uplinks (i.e. on fabric A) means 4 blades share one 4Gb/s link.... So, if you reduce the uplinks to 2, then you have 16 blades being distributed to 2 uplinks, so 8 blades per 4Gb/s uplink..which might very easy not be adequate
vcblades
Frequent Advisor

Fibre Channel uplinks - how many and how much?

FYI http://vinf.net/2008/04/09/how-does-an-hp-fibre-channel-virtual-connect-module-work/ http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c01702940/c01702940.pdf