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62.5 or 50 Multimode cable for 8gb SFP?
Hoping someone can confirm this for me. I am failry new to SANs, however I understand the benefits and limitations of the different FC cable types. We have engaged a consultant to configure our new array. The entire SAN fabric is running at 8Gb, however the array bus speed runs at 4Gb (Clariion CX4-120). Our consultant has used 62.5um cables for all connections, however I was under the impression that 50um cables would usually be used for this type of connectivity. The longest cable run is 5m between host, switch and array.
What I would like to know is if there is any performance loss using older style 62.5um cables for fast 8Gb connectivity. Or is the cable run so short that the core size has no impact?
RRR
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February 10th, 2011 01:00
Here it is !!! This is the document I was looking for !!!
http://www.cisco.com/en/US/prod/collateral/ps4159/ps6409/ps4358/product_data_sheet09186a00801bc698.html
Notice that for 50 micron there's OM2 and OM3 specs. 62.5 is always OM1.
62.5 micron OM1 @8Gb can transfer data over 21 meters
50 micron OM2 @8Gb can transfer data over 50 meters
50 micron OM3 @8Gb can transfer data over 150 meters
21 Meters seem enough, but suppose you leave your storage array rack to reach a server in another rack in another room or simply 3 rows further in your data center ? 21 Meters is easily reached.
I used to work in data centrers we had rows consisting of 10 racks per row and then 10 rows full of those. 21 Meters... We standardised on OM3.
You don't want to mix 62.5 OM1, 50 OM2 and 50 OM3. And if you also have long distance connections there's also 9 micron.... Keep the different sorts of cables as low as possible to avoid confusion.
RRR
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February 10th, 2011 01:00
I was completely off ! Here's a useful URL: http://www.cisco.com/en/US/prod/collateral/ps4159/ps6409/ps4358/data_sheet_c78-492690_ps5990_Products_Data_Sheet.html
RRR
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February 10th, 2011 01:00
Hello NRG,
50 is indeed the standard, but 62.5 is also allowed. There's no speed difference, since light travels at the same speed in 62.5 and 50 micron. However: distances that can be used with 62.5 are considerably shorter than with 50. Especially with 8Gb these distances are somewhat in the range of 10 meters or so. I'll look up the specs for you.
I think it was something like this using 50 micron:
1Gb = 500 meters
2Gb = 300 meters
4Gb = 150 meters
8Gb = 75 meters
With 62.5 it was something like:
1Gb = 300 meters
2Gb = 150 meters
4Gb = 750 meters
8Gb = 30 meters
Hmmmm, I'm not entirely sure.
Be right back with some Cisco URLs to be sure.
NRG1
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February 10th, 2011 02:00
Thanks for your time RRR - exactly the info I was looking for. So it seems I'm stuck @ 21m max distance without replacing all cables. I don't see that as an issue right now but who knows in future! The cables have already been paid for and I'm not going to start mixing types but as long as I'm getting full 8Gbps < 21m I'm happy.
Thanks again!
RRR
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February 10th, 2011 02:00
You're welcome
Although 21m is the max @8Gb, it's a lot easier to standardise @50 OM3 and leave the 62.5 for the LAN guys. This way you can easily distiguish what each cable is used for simply by looking at the specs printed on the cable.
I used to have this information online on www.50mu.net, but I'm building my BLOG site on there now, so the info is gone. Maybe I'll put a blog post on this topic on there when the site is to my satisfaction.
RRR
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February 10th, 2011 05:00
I just noticed that OM4 is available as well. OM4 is slightly better than OM3. the last URL I posted has that information as well.
hersh1
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February 10th, 2011 05:00
To add a little, I think OM3 and OM4 support 10 GbE if that is possibility in your environment.
RRR
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February 10th, 2011 07:00
In fact: I knew they were working on OM4, but didn't know it was out yet. I read that OM3 and OM4 support 10GbE. they don't even mention lower speeds on the OM3 and OM4 anymore....
Allen Ward
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March 4th, 2011 13:00
The qualification of not mixing cables should be cleared up a bit. While it certainly complicates things there is no technical reason not to have multiple cable types as long as you aren't mixing them in a single run. So if you are using patch cables with patch panels you would never want to use OM2 patch cables plugged into patch panels with OM1 trunking between them. It's the direct transition from one standard to another that causes issues.
Alternately, if you already have OM1 running from your array to your switches, and OM1 running from those switches to existing hosts, there is no technical reason not to use OM2 or OM3 runs from the same switches to other hosts. As long as the transition is done at an active device like a switch there is no problem. You still have the complication of multiple cable types in the configuration, but if you can manage that then you DO NOT have swap out all your cables just to get that one run you might come up against that has to go over 21m.
RRR
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March 9th, 2011 04:00
If you need to start from scratch OM2 or OM3 is probably the best choice (OM4 also exists), but if you already have OM1 in use, upgrading is hard. Decide for yourself when would be the best time to exchange the cables. Why exchange them ? For a standardized environment havong only OM3 would be best to avoid future mixups and errors where an OM1 simply can't cope with 50m distance.
If the core switches are nearby the storage you could use 62.5 to connect to those and OM3 for the hosts. It's what YOU want, so it depends on YOUR needs.