Tag Archives: optical

5-minute initial troubleshooting on Brocade equipment

Very often I get involved in cases whereby a massive amount of host logs, array dumps, FC and IP traces are taken which could easily add up to many gigabytes of data. This is then accompanied by a very synoptic problem description such as “I have a problem with my host, can you check?”.
I’m sure the intention is good to provide us all the data but the problem is the lack of the details around the problem. We do require a detailed explanation of what the problem is, when did it occur or is it still ongoing?

There are also things you can do yourself before opening a support ticket. In many occasions you’ll find that the feedback you get from us in 10 minutes results in either the problem being fixed or a simple workaround has made your problem creating less of an impact. Further troubleshooting can then be done in a somewhat less stressful time frame.

This example provides some bullet points what you can do on a Brocade platform. (Mainly since many of the problems I see are related to fabric issues and my job is primarily focused on storage networking.)

First of all take a look at the over health of the switch:

Provides an overview of the general components of the switch. These all need to show up HEALTHY and not (as shown here) as “Marginal”

Sydney_ILAB_DCX-4S_LS128:FID128:admin> switchstatusshow
Switch Health Report Report time: 06/20/2013 06:19:17 AM
Switch Name: Sydney_ILAB_DCX-4S_LS128
IP address: 10.XXX.XXX.XXX
SwitchState: MARGINAL
Duration: 214:29

Power supplies monitor MARGINAL
Temperatures monitor HEALTHY
Fans monitor HEALTHY
WWN servers monitor HEALTHY
CP monitor HEALTHY
Blades monitor HEALTHY
Core Blades monitor HEALTHY
Flash monitor HEALTHY
Marginal ports monitor HEALTHY
Faulty ports monitor HEALTHY
Missing SFPs monitor HEALTHY
Error ports monitor HEALTHY

All ports are healthy

Provides a general overview of logical switch status (no physical components) plus a list of ports and their status.

  • The switchState should alway be online.
  • The switchDomain should have a unique ID in the fabric.
  • If zoning is configured it should be in the “ON” state.

As for the ports connected these should all be “Online” for connected and operational ports. If you see ports showing “No_Sync” whereby the port is not disabled there is likely a cable or SFP/HBA problem.

If you have configured FabricWatch to enable portfencing you’ll see indications like here with port 75

Obviously for any port to work it should be enabled.

Sydney_ILAB_DCX-4S_LS128:FID128:admin> switchshow
switchName: Sydney_ILAB_DCX-4S_LS128
switchType: 77.3
switchState: Online
switchMode: Native
switchRole: Principal
switchDomain: 143
switchId: fffc8f
switchWwn: 10:00:00:05:1e:52:af:00
zoning: ON (Brocade)
switchBeacon: OFF
FC Router: OFF
Fabric Name: FID 128
Allow XISL Use: OFF
LS Attributes: [FID: 128, Base Switch: No, Default Switch: Yes, Address Mode 0]

Index Slot Port Address Media Speed State Proto
0 1 0 8f0000 id 4G Online FC E-Port 10:00:00:05:1e:36:02:bc “BR48000_1_IP146” (downstream)(Trunk master)
1 1 1 8f0100 id N8 Online FC F-Port 50:06:0e:80:06:cf:28:59
2 1 2 8f0200 id N8 Online FC F-Port 50:06:0e:80:06:cf:28:79
3 1 3 8f0300 id N8 Online FC F-Port 50:06:0e:80:06:cf:28:39
4 1 4 8f0400 id 4G No_Sync FC Disabled (Persistent)
5 1 5 8f0500 id N2 Online FC F-Port 50:06:0e:80:14:39:3c:15
6 1 6 8f0600 id 4G No_Sync FC Disabled (Persistent)
7 1 7 8f0700 id 4G No_Sync FC Disabled (Persistent)
8 1 8 8f0800 id N8 Online FC F-Port 50:06:0e:80:13:27:36:30
75 2 11 8f4b00 id N8 No_Sync FC Disabled (FOP Port State Change threshold exceeded)
76 2 12 8f4c00 id N4 No_Light FC Disabled (Persistent)

sfpshow slot/port
One of the most important pieces of a link irrespective of mode and distance is the SFP. On newer hardware and software it provides a lot of info on the overall health of the link.

With older FOS codes there could have been a discrepancy of what was displayed in this output as to what actually was plugged in the port. The reason was that the SFP’s get polled so every now and then for status and update information. If a port was persistent disabled it didn’t update at all so in theory you plug in another SFP but sfpshow would still display the old info. With FOS 7.0.1 and up this has been corrected and you can also see the latest polling time per SFP now.

The question we often get is: “What should these values be?”. The answer is “It depends”. As you can imagine a shortwave 4G SFP required less amps then a longwave 100KM SFP so in essence the SFP specs should be consulted. As a ROT you can say that signal quality depends ont he TX power value minus the link-loss budget. The result should be withing the RX Power specifications of the receiving SFP.

Also check the Current and Voltage of the SFP. If an SFP is broken the indication is often it draws no power at all and you’ll see these two dropping to zero.

Sydney_ILAB_DCX-4S_LS128:FID128:admin> sfpshow 1/1
Identifier: 3 SFP
Connector: 7 LC
Transceiver: 540c404000000000 2,4,8_Gbps M5,M6 sw Short_dist
Encoding: 1 8B10B
Baud Rate: 85 (units 100 megabaud)
Length 9u: 0 (units km)
Length 9u: 0 (units 100 meters)
Length 50u (OM2): 5 (units 10 meters)
Length 50u (OM3): 0 (units 10 meters)
Length 62.5u:2 (units 10 meters)
Length Cu: 0 (units 1 meter)
Vendor Name: BROCADE
Vendor OUI: 00:05:1e
Vendor PN: 57-1000012-01
Vendor Rev: A
Wavelength: 850 (units nm)
Options: 003a Loss_of_Sig,Tx_Fault,Tx_Disable
BR Max: 0
BR Min: 0
Serial No: UAF110480000NYP
Date Code: 101125
DD Type: 0x68
Enh Options: 0xfa
Status/Ctrl: 0x80
Alarm flags[0,1] = 0x5, 0x0
Warn Flags[0,1] = 0x5, 0x0
Alarm Warn
low high low high
Temperature: 25 Centigrade -10 90 -5 85
Current: 6.322 mAmps 1.000 17.000 2.000 14.000
Voltage: 3290.2 mVolts 2900.0 3700.0 3000.0 3600.0
RX Power: -3.2 dBm (476.2uW) 10.0 uW 1258.9 uW 15.8 uW 1000.0 uW
TX Power: -3.3 dBm (472.9 uW) 125.9 uW 631.0 uW 158.5 uW 562.3 uW

State transitions: 1
Last poll time: 06-20-2013 EST Thu 06:48:28

For link state counters this is the most useful command in the switch however there is a perception that this command provides a “silver” bullet to solve port and link issues but that is not the case. Basically it provides a snapshot of the content of the LESB (Link Error Status Block) of a port at that particular point in time. It does not tell us when these counters have accumulated and over which time frame. So in order to create a sensible picture of the statuses of the ports we need a baseline. This baseline can be created to reset all counters and start from zero. To do this issue the “statsclear” command on the cli.

There are 7 columns you should pay attention to from a physical perspective.

enc_in – Encoding errors inside frames. These are errors that happen on the FC1 with encoding 8 to 10 bits and back or, with 10G and 16G FC from 64 bits to 66 and back. Since these happen on the bits that are part of a data frame that are counted in this column.

crc_err – An enc_in error might lead to a CRC error however this column shows frames that have been market as invalid frames because of this crc-error earlier in the datapath. According to FC specifications it is up to the implementation of the programmer if he wants to discard the frame right away or mark it as invalid and send it to the destination anyway. There are pro’s and con’s on both scenarios. So basically if you see crc_err in this column it means the port has received a frame with an incorrect crc but this occurred further upstream.

crc_g_eof – This column is the same as crc_err however the incoming frames are NOT marked as invalid. If you see these most often the enc_in counter increases as well but not necessarily. If the enc_in and/or enc_out column increases as well there is a physical link issue which could be resolved by cleaning connectors, replacing a cable or (in rare cases) replacing the SFP and/or HBA. If the enc_in and enc_out columns do NOT increase there is an issue between the SERDES chip and the SFP which causes the CRC to mismatch the frame. This is a firmware issue which could be resolved by upgrading to the latest FOS code. There are a couple of defects listed to track these.

enc_out – Similar to enc_in this is the same encoding error however this error was outside normal frame boundaries i.e. no host IO frame was impacted. This may seem harmless however be aware that a lot of primitive signals and sequences travel in between normal data frame which are paramount for fibre-channel operations. Especially primitives which regulate credit flow. (R_RDY and VC_RDY) and signal clock synchronization are important. If this column increases on any port you’ll likely run into performance problems sooner or later or you will see a problem with link stability and sync-errors (see below).

Link_Fail – This means a port has received a NOS (Not Operational) primitive from the remote side and it needs to change the port operational state to LF1 (Link Fail 1) after which the recovery sequence needs to commence. (See the FC-FS standards specification for that)

Loss_Sync – Loss of synchronization. The transmitter and receiver side of the link maintain a clock synchronization based on primitive signals which start with a certain bit pattern (K28.5). If the receiver is not able to sync its baud-rate to the rate where it can distinguish between these primitives it will lose sync and hence it cannot determine when a data frame starts.

Loss_Sig – Loss of Signal. This column shows a drop of light i.e. no light (or insufficient RX power) is observed for over 100ms after which the port will go into a non-active state. This counter increases often when the link-loss budget is overdrawn. If, for instance, a TX side sends out light with -4db and the receiver lower sensitivity threshold is -12 db. If the quality of the cable deteriorates the signal to a value lower than that threshold, you will see the port bounce very often and this counter increases. Another culprit is often unclean connectors, patch-panels and badly made fibre splices. These ports should be shut down immediately and the cabling plant be checked. Replacing cables and/or bypassing patch-panels is often a quick way to find out where the problem is.

The other columns are more related to protocol issues and/or performance problems which could be the result of a physical problem but not be a cause. In short look at these 7 columns mentioned above and check if no port increases a value.

too_short/too_long – indicates a protocol error where SOF or EOF are observed too soon or too late. These two columns rarely increase.

bad_eof – Bad End-of-Frame. This column indicates an issue where the sender has observed and abnormality in a frame or it’s transceiver whilst the frameheader and portions of the payload where already send to its destination. The only way for a transceiver to notify the destination is to invalidate the frame. It truncates the frame and add an EOFni or EOFa to the end. This signals the destination that the frame is corrupt and should be discarded.

F_Rjt and F_Bsy are often seen in Ficon environments where control frames could not be processes in time or are rejected based on fabric configuration or fabric status.

c3timout (tx/rx) – These are counters which indicate that a port is not able to forward a frame in time to it’s destination. These either show a problem downstream of this port (tx) or a problem on this port where it has received a frame meant to be forwarded to another port inside the sames switch. (rx). Frames are ALWAYS discarded at the RX side (since that’s where the buffers hold the frame). The tx column is an aggregate of all rx ports that needs to send frames via this port according to the routing tables created by FSPF.

pcs_err – Physical Coding Sublayer – These values represent encoding errors on 16G platforms and above. Since 16G speeds have changed to 64/66 bits encoding/decoding there is a separate control structure that takes care of this.

As a best practise is it wise to keep a trace of these port errors and create a new baseline every week. This allows you to quickly identify errors and solve these before they can become an problem with an elongated resolution time. Make sure you do this fabric-wide to maintain consistency across all switches in that fabric.

Sydney_ILAB_DCX-4S_LS128:FID128:admin> porterrshow
frames enc crc crc too too bad enc disc link loss loss frjt fbsy c3timeout pcs
tx rx in err g_eof shrt long eof out c3 fail sync sig tx rx err
0: 100.1m 53.4m 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1: 466.6k 154.5k 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
2: 476.9k 973.7k 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
3: 474.2k 155.0k 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Make sure that all of these physical issues are solved first. No software can compensate for hardware problems and all OEM support organizations will give you this task anyway before commencing on the issue.

In one of my previous articles I wrote about problems, the cause and the resolution of physical errors. You can find it over here


Brocade FOS 7.1 and the cool features

After a very busy couple of weeks I’ve spent some time to dissect the release notes of Brocade FOS 7.1 and I must say there are some really nice features in there but also some that I REALLY think should be removed right away.

It may come to no surprise that I always look very critical to whatever come to the table from Brocade, Cisco and others w.r.t. storage networking. Especially the troubleshooting side and therefore the RAS capabilities of the hardware and software have a special place in my heart so if somebody screws up I’ll let them know via this platform. 🙂
So first of all some generics. FOS 7 is supported on the 8 and 16G platforms which cover the Goldeneye2,Condor2 and Condor 3 ASICs plus the AP blades for encryption, SAN extension and FCoE. (cough, cough)….Be aware that it doesn’t support the blades based on the older architecture such as the FR4-18i and FC10-6 (which I think was never bought by anyone.)  Most importantly this is the first version to support the new 6520 switch so if you ever think of buying one it will come shipped with this version installed. 
As for the software features Brocade really cranked up the RAS features. I especially do like the broadening of the scope for D-ports (diagnostics port) to include ICL ports but also between Brocade HBA’s and switch ports. One thing they should be paying attention to though is that they should sell a lot more of these. :-). Also the characteristics of the test patterns such as test duration, frame-sizes and number of frames can now be specified. Also FEC (Forward Error Correction) has been extended to access gateways and long distance ports which should increase stability w.r.t. frame flow. (It still doesn’t improve on signal levels but that is a hardware problem which cannot be fixed by software).
There are some security enhancements for authentication such as extended LDAP and TACACS+ support.
The 7800 can now be used with VF albeit not having XISL functionality. 
Finally the E_D_TOV FC timer value is propagated onto the FCIP complex. What this basically means that previously even though an FC frame had long timed-out according to FC specs (in general 2 seconds) it could still exist on the IP network in a FCIP packet. The remote FC side would discard that frame anyway thus wasting valuable resources. With FOS 7.1 the FCIP complex on the sending side will discard the frame after E_D_TOV has expired.
One of the most underutilised features (besides Fabric Watch) is FDMI (Fabric Device Management Interface). This is a separate FC service (part of the new FC-GS-6 standard) which can hold a huge treasure box of info w.r.t. connected devices. As an example:
FDMI entru
        switch:admin> fdmishow
        Local HBA database contains:
          Ports: 1
              Port attributes:
                FC4 Types: 0x0000010000000000000000000000000000000000000000000000000000000000
                Supported Speed: 0x0000003a
                Port Speed: 0x00000020
                Frame Size: 0x00000840
                Device Name: bfa
                Host Name: X3650050014
                Node Name: 20:00:8c:7c:ff:01:eb:00
                Port Name: 10:00:8c:7c:ff:01:eb:00
                Port Type: 0x0
                Port Symb Name: port2
                Class of Service: 0x08000000
                Fabric Name: 10:00:00:05:1e:e5:e8:00
                FC4 Active Type: 0x0000010000000000000000000000000000000000000000000000000000000000
                Port State: 0x00000005
                Discovered Ports: 0x00000002
                Port Identifier: 0x00030200
          HBA attributes:
            Node Name: 20:00:8c:7c:ff:01:eb:00
            Manufacturer: Brocade
            Serial Number: BUK0406G041
            Model: Brocade-1860-2p
            Model Description: Brocade-1860-2p
            Hardware Version: Rev-A
            Driver Version:
            Option ROM Version:
            Firmware Version:
            OS Name and Version: Windows Server 2008 R2 Standard | N/A
            Max CT Payload Length: 0x00000840
            Symbolic Name: Brocade-1860-2p | | X3650050014 |
            Number of Ports: 2
            Fabric Name: 10:00:00:05:1e:e5:e8:00
            Bios Version:
            Bios State: TRUE
            Vendor Identifier: BROCADE
            Vendor Info: 0x31000000
and as you can see this shows a lot more than the fairly basic nameserver entries:
N    8f9200;      3;21:00:00:1b:32:1f:c8:3d;20:00:00:1b:32:1f:c8:3d; na
    FC4s: FCP 
    NodeSymb: [41] “QLA2462 FW:v4.04.09 DVR:v8.02.01-k1-vmw38”
    Fabric Port Name: 20:92:00:05:1e:52:af:00 
    Permanent Port Name: 21:00:00:1b:32:1f:c8:3d
    Port Index: 146
    Share Area: No
    Device Shared in Other AD: No
    Redirect: No 
    Partial: No
    LSAN: No
Obviously the end-device needs to support this and it has to be enabled. (PLEASE DO !!!!!!!!) It’s invaluable for troubleshooters like me….
One thing that has bitten me a few times was the SFP problem. There has long been a problem that when a port was disabled and a new SFP was plugged in the switch didn’t detect that until the port was enabled and it had polled for up-to-date information. In the mean time you could get old/cached info of the old SFP including temperatures, db values, current, voltage etc.. This seems to be fixed now so thats one less thing to take into account.
Some CLI improvements have been made on various commands with some new parameters which lets you filter and select for certain errors etc.
The biggest idiocracy that has been made with this version is to allow the administrator change the severity level of event-codes. This means that if you have a filter in BNA (or whatever management software you have) to exclude INFO level messages but certain ERROR or CRITICAL messages start to annoy you you could change the severity to INFO and thus they don’t show up anymore. This doesn’t mean th problem is less critical so instead of just fixing the issue we now just pretend it’s not there. From a troubleshooting perspective this is disastrous since we look at a fair chuck of sup-saves each day and if we can’t rely on consistency in a log file it’s useless to have a look in the first place. Another one of those is the difference in deskew values on trunks when FEC is enabled. Due to a coding problem these values can differ up to 40 therefore normally depicting a massive difference in cable length. Only by executing a d-port analysis you can determine if that is really the case or not. My take is that they should fix the coding problem ASAP.  
A similar thing that has pissed me off was the change in sfpshow output. Since the invention of the wheel this has been the worst output in the brocade logs so many people have scripted their ass off to make it more readable.
Normally it looks like this:
Slot  1/Port  0:
Identifier:  3    SFP
Connector:   7    LC
Transceiver: 540c404000000000 2,4,8_Gbps M5,M6 sw Short_dist
Encoding:    1    8B10B
Baud Rate:   85   (units 100 megabaud)
Length 9u:   0    (units km)
Length 9u:   0    (units 100 meters)
Length 50u:  5    (units 10 meters)
Length 62.5u:2    (units 10 meters)
Length Cu:   0    (units 1 meter)
Vendor Name: BROCADE         
Vendor OUI:  00:05:1e
Vendor PN:   57-1000012-01   
Vendor Rev:  A   
Wavelength:  850  (units nm)
Options:     003a Loss_of_Sig,Tx_Fault,Tx_Disable
BR Max:      0   
BR Min:      0   
Serial No:   UAF11051000039A 
Date Code:   101212  
DD Type:     0x68
Enh Options: 0xfa
Status/Ctrl: 0xb0
Alarm flags[0,1] = 0x0, 0x0
Warn Flags[0,1] = 0x0, 0x0
                                          Alarm                  Warn
                                   low        high       low         high
Temperature: 31      Centigrade    -10         90         -5          85
Current:     6.616   mAmps          1.000      17.000     2.000       14.000 
Voltage:     3273.4  mVolts         2900.0      3700.0    3000.0       3600.0 
RX Power:    -2.8    dBm (530.6uW) 10.0   uW 1258.9 uW   15.8   uW  1000.0 uW
TX Power:    -3.3    dBm (465.9 uW)125.9  uW   631.0  uW  158.5  uW   562.3  uW
and that is for every port which basically makes you nuts.
So with some bash,awk,sed magic I scripted the output to look like this:
Port  Speed   Long  Short  Vendor     Serial            Wave   Temp   Current  Voltage   RX-Pwr   TX-Pwr
wave wave number Length
1/0 8G NA 50 m BROCADE UAF11051000039A 850 31 6.616 3273.4 -2.8 -3.3
1/1 8G NA 50 m BROCADE UAF110510000387 850 32 7.760 3268.8 -3.6 -3.3
1/2 8G NA 50 m BROCADE UAF1105100003A3 850 30 7.450 3270.7 -3.3 -3.3
From a troubleshooting perspective this is so much easier since you can spot issues right away.
Now with FOS 7.1.x the FOS engineers screwed up the SFPshow output which inherently screwed up my script which necessitates a load more work/code/lines to get this back into shape. The same thing goes for the output on the number of credits on virtual channels.
Pre-FOS 7.1 it looks like this:
C:—— blade port 64: E_port ——————————————
C:0xca682400: bbc_trc                 0004 0000 002a 0000 0000 0000 0001 0001 
With FOS 7.1 it looks like this:
bbc registers
0xd0982800: bbc_trc                 20   0    0    0    0    0    0    0    
(Yes, hair pulling stuff, aaarrrcchhhh)
Some more good things. The fabriclog now contains the direction of link resets. Previously we could only see an LR had occurred but we didn’t see who initiated it. Now we can and have the option to figure out in which direction credit issues might have been happening. (phew..)
The CLI history is now also saved after reboots and firmware-upgrades. Its been always a PITA to figure out who had done what at a certain point-in-time. This should help to try and find out.
One other very useful thing that has been added and it a major plus in this release is the addition of the remote WWNN of a switch in the switchshow and islshow output even when the ISL has segmented for whatever reason. This is massively helpful because normally you didn’t have a clue what was connected so you also needed to go through quite some hassle and check cabling or start digging through the portlogdump with some debug flags enabled. Always a troublesome exercise. 
The bonus points from for this release is the addition of the fabretrystats command. This gives us troubleshooters a great overview of statistics of fabric events and commands. 
0        0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
69       0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
71       0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
79       0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
131      0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
140      0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
141      0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
148      0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
149      0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
168      0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
169      0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
174      0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
175      0    0    0      0    0    0    0    0    0    0    0    0        0    0    0    0    0    0        
This release also fixes a gazillion defects so its highly advisable to get to this level better sooner than later. Check with your vendor for the latest supported release.
So all in all good stuff but some things should be reverted, NOW!!!. and PLEASE BROCADE: don’t screw up more output in such a way it breaks existing analysis scripts etc…

The importance of clean fibre optics

I attended Cisco Live this week in Melbourne. Since it was very close to home and Cisco was kind enough to provide me with an entry ticket. (Many thanks for this.)

While strolling around the expo floor I ran into the nice people from Fluke Networks who were showing their testing equipment and of course I was very interested in the optical side of the fence. (I haven’t seen wireless storage networks yet so I’ll save that part of their impressive toolkit for later. :-)).

Since I’m doing troubleshooting as a day to day job I see many issues which have characteristics of a physical nature. This can be a bad cable, patch panel, SFP or anything in that nature.

Just when I wanted to start this blog post I saw that my Melbournian buddy  Anthony Vandewerdt just beat me to it and wrote the article “Semmelweiss could see the problem” in which he described the problem of unclean cables and where it might lead to.  (read this first and then come back here.)

In order to complement that article I’ll try to explain why this is so important.

I’m pretty sure that everyone these days know that computers work with bits which are either a 1 or 0. To be able to communicate with other computers (or devices in general) we use transmission of bits with either an on or off signal whether this being an electrical current or an optical wave. Electrical use has the nasty habit that the energy is partially stored in the capacitance of the electrical cable so it has a certain drop zone before it becomes a capacitor with 0 value. You can see this very well if you use a laptop charger with a small led. When you unplug it from the wall-socket it takes a couple of seconds before the current is completely gone from the capacitors in the transformer. This is also one of the primary reasons FC uses a 8b/10b encoding decoding schema to keep a balanced DC value.

The optical to electrical transformers have the same issue albeit not being in the cable itself but more in the physics characteristics of the circuitry. There is a certain fall-off and ramp-up time before current becomes completely zero and completely one respectively. This is very important since this depicts when a receiver should determine if the incoming bit should be seen as a 1 or are 0.

The optics people and companies represented in IEEE and T11-2 do write up the official metrics so this is all being done for you. There is nothing on a switch, array or other network equipment where you can tune this.

The measurement and characteristics of a signal can be measured with an oscillator. The result you see looks like this:

The blue lines show the voltage on the oscillator and this shows the, so called, eye-pattern. The hexagon in the middle is determine by the folks of IEEE and T11-2 and can be loaded as a software feature for ease of use on most equipment. (Note: be aware that this differs per technology and optical characteristic like FC, Ethernet, DWDM etc. )
The above picture shows a perfect eye-pattern since it show that the ramp-up time (from the bottom blue line to the top) is way before the “decision point” on becoming a 1 and the fall-off time is way after the decision point of becoming a 0.
“So what does this have to do with my fibre-cable” you may ask.
When connectors are not clean the light may be reflected back in to the cable causing jitter. It is this jitter that can significantly close the eye-pattern to a point where the receiver can no longer determine if an incoming light should be determined as a 1 or 0. The below picture show that this comes pretty close.
By default it will keep the same value it had on the previous clock cycle. This means that a one remains a 1 even though it actually should have been a 0 and vice versa. The result will be that the bitstream from the receiver buffer into the serdes chip will be incorrect thereby causing a decoding error. For FC it means that the er_enc_out or er_enc_in value on the LESB (Link Error Status Block) is incremented by one (depending if the 10-bit transmission word was part of a FC frame or not). On a Brocade switch in the porterrshow output this is shown in the enc_in or enc_out column.
If this happens on a bit which was part of a, normally valid, FC frame the frame now contains an invalid byte. If we not would have a fall-back mechanism this would have led to an invalid byte being send to the operating system and application causing corruption and even system failures. Since we also do a CRC check on the entire frame the destination port will discard it entirely and the upper layer SCSI stack (or whatever protocol resides on the FC4 layer) retry the IO.
The problem is that with distance you get loss of power (remember that light is measured in db’s). Depending on the type of cable (OM1,2,3,4) this budget loss on the cable is fixed. Every connection or splice (two optical cables welded together) adds to the link loss and decreases the optical power received on the other side of the link. The problem with dirty connections is that it significantly decreases the optical power which can cause the problem that the value in db the receiver can detect falls outside the specification of that particular SFP. This can cause link losses and port flapping causing all sorts of other nasty issues.
The link loss budget can be calculated based on the launch power of the transmitter, the number of connectors and splices in the cable-plant plus the margin on the receiver side.If this all falls below the receiver sensitivity mark the receiver will drop the link and the ports will go offline.
On a Brocade switch you can see the transmitter and receiver value with the “sfpshow” command:
The specifications of the SFP determine what the transmit and receive power should be. If the actual values of the RX power fall outside the specification of the SFP you should start to look at you cable’s, connectors and start cleaning them. If this doesn’t help there might be another problem like a crack in the cable or the SFP has a broken laser. In this case either replace the cable and/or SFP.
Hope this may help to explain why you might see strange things in your fibre channel network if the connectors are not clean and your support organisation is really stressing to fix and maintain your cable plant. I did mention I work in support and I see many connectivity issues resulting in flapping ports, overall performance issues and even data-loss or corruption.
If you want to know the characteristics of optical cables or SFP’s I suggest you have a look at the JDSU, Finisar or Avago websites. Also check out the FOA Youtube channel who uploaded some nice video’s which explain in detail the ins and outs of fibre optics.

The end of spinning disks (part 2)

Maybe you found the previous article a bit hypothetical and is not substantiated by facts but merely some guestimations?

To put some beef into the equation I’ll try to substantiate it with some simple calculations. Read on.

As shown in Cornell Uni’s report the expected amount of data generated will reach 1700 exabytes in 2011 with an additional 2500 in 2012. 1700 exabytes equates to 1 trillion, 700 billiard gigabytes in EU notation (say what…., look here)

So number-wise it looks like this: 1.700.000.000.000 GB

The average capacity of a disk drive in 2011 is around 1400 GB (the average of enterprise drives with high RPM of 600GB + the largest capacity wise commercially available for enterprise environments HDD of 2TB).In consumer land WD has a 6TB drive but these will not become mainstream until the end of 2011 or beginning 2012 . Maybe storage vendors will use the 3 and 4 TB versions but I do not have visibility of that currently.

1700EB / 1400GB = disk drives are needed to store this amount of information. (Ohh, in 2012 we need 1.785.714.286 units :-))

This leads us to have a look at production capabilities and HD vendors. Currently there are two major vendors in the HDD market. Seagate (which shipped 50 million HDD in FQ3 2011) and WD shipping 49 million. (Seagate acquired HGST and WD is talking to the HDD division of Samsung) Those 4 companies combined have a production capacity of around 150 million diskdrives per quarter. This means on an annual basis a shortage of : – 600.000.000 = 614.285.714 HDD’s
So who says the HDD business isn’t a healthy one? 🙂

OK, I agree, not everything is stored on HDD and the offload to secondary media like DVD,BlueRay,tape etc will cut a significant piece out of this pie however the instantiation of new data will primarily be done on HDD’s. Adoption of newer, larger capacity HDD is restricted for enterprise use because the access density is getting too high which equates to higher latency and lower performance which is not acceptable in these kind of environments.

This means new techniques will need to be adopted in all areas. From a performance perspective a lot can be gained with SSD’s (Solid State Drives) which have extremely good read performance but still lack somewhat in write performance as well as long term reliability. I’m sure over time this will be resolved. SSD will however not fill the capacity gap needed to accommodate the data growth.

As mentioned before my view is that this gap can and will be filled by advanced 3D optical media which provides new levels of capacity, performance, reliability and cost savings.

I’m open for constructive comments.


The end of spinning disks

Did you ever wonder how long this industry will rely on spinning disk? I do and I think that within 5 to 10/15 years we’ve reached the end of the abilities of disks to keep up with demand and data growth ratios. A report from Andrey V Makarenko of Cornell University estimates that around 1700 Exabytes (yes EXA-bytes) will be generated in 2011 alone with growth rates to over 2500 EXAbytes next year.

With new technologies invented and implemented in science, space exploration, health care and last but not least consumer electronics this growth ratio will increase exponentially. Although disk drive technology has kept pretty much pace with Moore’s law you can see the advances in development of this technology is declining. Rotational speed has been steady for years and the edges of perpendicular recording have almost been reached. This means that within the foreseeable future there will be a flipping point were demand will outgrow the capacity. Even if production facilities would be increased to keep up with demand, do we as society want to have these massive infrastructures which are very expensive to build and maintain as well as having a huge burden on our environment. So were does this leave us, do we have to stop generating data or generate it in a far more efficient way or should we also combine this with aggressive data life cycle management. I wrote an article earlier in this blog which shows how this could be achieved and it doesn’t take a scientist to understand it.
To go back to the subject there are talks that SSD will take over a significant amount of magnetic based drives and maybe it is so however it still lacks on reliability in one form or another. I’m sure this will be resolved in the not so distant future however will this technology be as cost effective as spinning disks have been in the last decades. I think this will take a significant amount of time to reach that point. So where do we go from here? It is my take that in addition to the uptake of SSD based drives significant advances will be made in 3D optical storage. This will not only allow for massive increase in capacity per cubic inch but also a reduction in cost, energy as well as a massive increase in performance.
Advancements in laser technology and photonic behavior as well as optical media will clear the pathway of adoption into data-centers the moment this will become commercially attractive.

There are numerous scientific studies as well as commercial entities working on this type of technology and due to market demand add significant pressure on the development of it. Check out this wikipedia article on 3D optical storage to get some more information around the technicalities.

Let me know your opinion.

Erwin van Londen