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Ask the Expert: SAN (Connectrix), FC Connectivity Recommendations and Best Practices
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Welcome to this Ask the Expert discussion. This session will address the topic of “SAN (Connectrix), FC Connectivity Recommendations and Best Practices". We will discuss best practice in storage networks FC networks (SAN) with the goal to obtain better performance and optimal configuration. In addition, we will answer questions about administration, planning and SAN configuration.
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RobertoAraujo1
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February 2nd, 2015 06:00
Welcome to our newest ATE session on ECN. We'd like to open this discussion for replies. Let's make of this an opportunity to respectfully engage our experts with your questions, comments or ideas. Have a great experience!
dynamox
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February 2nd, 2015 08:00
Felipe,
Do you see a lot of customers adopting SmartZoning ?
Thanks
felipon1
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February 3rd, 2015 05:00
Hi dynamox ,
First off thanks for your query. The fact is that, although this feature is pretty useful, not many customers use it: mainly customers with a big SAN to manage take the step to introduce Smart Zoning.
For those of you who are not familiar with the concept of Smart Zoning, the following link provides a nice description of this feature introduced by Cisco in NX-OS 5.2(6).
By using Smart Zoning, the size and manageability of zonesets can be drastically decreased, specially when using clusters that share targets (storage ports) among several Initiators (server HBAs). With Smart Zoning, you can configure a single zone containing all the Initiators and targets in the same cluster (eg ESX farm) and the switch itself prevents the Initiators from seen each other even though they're in the same zone.
Rgds,
Felipe
dynamox
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February 3rd, 2015 05:00
I don't have a big SAN (one 9513 core and a few 9148 edges) and i have been using SmartZoning for 2 years now. It is the best thing that has happened to zoning in a long time . It was very easy to enable SZ on a running VSAN too, "traditional zones co-exist with SmartZones in the same zoneset just fine.
Anonymous
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February 4th, 2015 02:00
Hi Felipe,
a customer has upgraded to FOS 7.x, and needs to know if, with the new version, they still need to take care to manually config the parameter fillword to value = 3.
Thanks mate!
Manu
felipon1
96 Posts
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February 4th, 2015 08:00
Good evening Manu,
That's a good one, because there is a little bit of confusion with it. The answer to that question is:
The fillword is a FC primitive [in plain language, pre-defined frames] used to keep the link synchronized. It became renowned when Brocade introduced the family of switchs that supported 8G. When working at 8G, the FC standard states that the fillword to use is ARB (whilst previously it was IDLE). With 8G Brocade products, this fillword has to be manually configured and when Brocade released the new set of 16G switchs, the fillword is automatically configured, so in a few years time, we will forget about this parameter and live happily oblivious again.
When it comes to EMC products, the recommendation is to configure the fillword with a value of 3 when working at 8G.
Rgds,
Felipe
Alex_T1
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February 4th, 2015 13:00
Hello Felipe
What is the main benefits of using ISL trunking?
How does exactly load balance work with and without trunking license?
Also you mentioned smart zoning before. Is there any smart zoning analog in brocade san switches?
felipon1
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February 6th, 2015 02:00
Hello Alex.T ,
According to Brocade documentation The trunking feature optimizes the use of bandwidth by allowing a group of inter-switch links (ISLs) to merge into a single logical link....
In practice, the main benefit of trunking is that, it appears a single logical ISL, and this simplifies the routing tables inside the fabric, and most important, when there is a failure/activation of one of the ISLs, no new calculations need to be performed, and thus the traffic disruption is minimal. In the same situation, without trunking, there is a disruption until the routes are re-calculated.
When it comes to load balancing (and the use of bandwith) between switchs, it depends on the Routing policy configured on the switch. There are mainly 2 routing policies:
Initially, when only port-based routing was available, if you had ,e.g 3 ISLs, you could have one of them heavily used whilst the other two were not used at all. In that case, trunking was very beneficial as it overtook that potential congestion situation by creating a 3-isl trunk. But since exchange-based routing was released, this situation disappeared and traffic is evenly balanced among all the ISLs. So, as far as load balance is concerned, trunking does not offer a big improvement.
If you meant the difference in load balancing withing the ISLs that form a trunk, with and without trunking licences, here there is indeed a significant difference:
Hope it answers your query.
rgds,
Felipe
Harshak
52 Posts
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February 7th, 2015 17:00
Why do we need more buffer credits on ISL ports compared to normal Host/Storage Ports ?
felipon1
96 Posts
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February 8th, 2015 02:00
Hi there koppuru
Thanks for posting this question. I consider that there are 3 main reasons to have a larger number of buffer-to-buffer credits (BBC) on an ISL:
Best regards,
Felipe
dynamox
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February 8th, 2015 09:00
Felipe,
to piggy back on koppuru questions, is there a formula how to calculate B2B credits. Anything specific for DWDM versus FCIP ?
Thanks
felipon1
96 Posts
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February 10th, 2015 03:00
Hi again dynamox
I'm glad you asked it because the B2B credits (or BBC) is a matter I see many issues with.
In order to calculate the amount of required BBCs, Brocade uses the following formula:
Number of BBCs = (Distance(in Km) * LinkSpeed / 2) + 6
That '6' at the end of the formula, are 6 BBC reserved for Class-F traffic.
But we have to be careful since this formula calculates the number of buffer-to-buffer credits based on a full frame size (2148 KB), it doesn't take into account the average size of the frames going through the ISL. Historically, due to this fact, I have seen many issues when configuring extended ISLs, since by default many (Brocade) customers configure their extended ISLs with LD mode, and LD mode uses the above formula.
LD mode is one of the available config modes for extended ISLs in Brocade, it is very used since it automatically estimates the link length and calculate the required BBCs based on that distance. But, as I said before, it performs its calculations considering that the average size of the frames is 2 KB (2148 KB actually). In practice, the average frame size is always smaller than 2 KB, and thus more buffers that the calculated with that formula (and applied by LD mode) are required.
In order to take the average size into consideration for the calculation, we have to add the following to the formula:
Number of BBCs = [(Distance(in Km) * LinkSpeed / 2) * ( / )] + 6
Based on the above formula, I performed the below table:
LINK SPEED
TAMAÑO MEDIO DE TRAMA
DISTANCE
BB CREDITS REQUIRED (-6)
1G
2 KB
100 Km
50
2G
2 KB
100 Km
100
4G
2 KB
100 Km
200
8G
2 KB
100 Km
400
1G
2 KB
200 Km
100
2G
2 KB
200 Km
200
4G
2 KB
200 Km
400
8G
2 KB
200 Km
800
1G
1 KB
100 Km
100
2G
1 KB
100 Km
200
4G
1 KB
100 Km
400
8G
1 KB
100 Km
800
1G
1 KB
200 Km
200
2G
1 KB
200 Km
400
4G
1 KB
200 Km
800
8G
1 KB
200 Km
1600
Checking this table, we get the following info:
By using this table we can easily calculate the number of required BB Credits.
With FOS 6 and below, the only way to configure the BBC in Brocade was by indicating the desired distance at the setup of the extended ISL (in LS mode) and this led to some confusion. Fortunately for us, with FOS 7 Brocade included a BBC calculator in which you introduce the link length, speed and average size and it automatically calculates the required BBC for you.
DS6510b-1:FID128:root> portbuffercalc 0 -distance 100 -speed 4 -framesize 2048
206 buffers required for 100km at 4G and framesize of 2048bytes
DS6510b-1:FID128:root> portbuffercalc 0 -distance 100 -speed 4 -framesize 1024
406 buffers required for 100km at 4G and framesize of 1024bytes
It is also easier to calculate the average frame size, since command portbuffershow shows the average frame size and the average buffer usage:
User Port Lx Max/Resv Avg Buffer Usage & FrameSize Buffer Needed Link Remaining
Port Type Mode Buffers Tx Rx Usage Buffers Distance Buffers
---- ---- ---- ------- ---------------------------- ------ ------- --------- ---------
0 E LS 206 29(1172) 35(1396) 206 206 100km
Additionally, the command used to configure BBC on Brocade (portcfglongdistance) has been improved and now we can introduce the average frame size as well. So, when it comes to Brocade switchs, FOS 7 has make a big breakthrough with Extended ISLs.
On the other hand, Cisco is clearer on this situation and by default, it provides the ISL with a whole bunch (the number depends on the ASIC/blade model) of BBCs (or B2B credits if you prefer), so usually configuring an extended ISL on a Cisco switch is pretty easy and straightforward. But in case you need to modify the amount of B2B, the table and formula is also valid.
Kind regards,
Felipe
javirodz
8 Posts
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February 11th, 2015 13:00
Felipe, hay alguna diferencia en performance cuando se usa una zona "single initiator - multiple targets" vs. "single initiator - single target"?
Gracias
dynamox
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February 11th, 2015 19:00
it is common courtesy to post in English if you see everyone else contribute in English.
dynamox
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February 11th, 2015 19:00
please post in English