Disk Subsystem - Storage Basics-2

In storage, the directly connected small disks are replaced by large storage subsystems connected via storage network.  It has the flexibility to assigned hard disk to the servers as per the availability. Servers are either connected to Disk subsystem directly or indirectly via SAN ( storage Area Network).

There are below advantages of using storage system.

1. High Availability:- Data will remain available if any of the disk fails. With the help of RAID configuration we can provide 100% data backup and fault tolerance.

2. High performance:-  All the disk are available to the servers and they can get the hard disk as and when they need it.

3. Instant Copy: - Controllers are responsible to perform the parallel write of data to multiple disks to increase the write speed.

4. Remote mirroring:- RAID controllers are available to provide high fault tolerance by copying the data to multiple disks.

Disk Subsystem:-  It consists of storage devices like Hard Disks, Tapes and Controllers. There can be a disk subsystem where controller is not present.

 JBOD (Just bunch of Disk) is the low cost storage subsystem in which all the disks are placed in single enclosure with common power supply. There is no controller present in JBOD. It is used for small deployments.

Components of Disk Subsystem-

•   Storage Devices: - Hard disk and tapes are used to store data and to increase the fault tolerance we may need the controller to handle the individual disks.

•     Controllers: - It’s like brain of the complete disk subsystem and makes the entire cluster of small disks as one big virtual disk. RAID (Redundant Array of independent disks) Controllers controls the disks subsystem and provide instant copy and remote mirroring features to provide high fault tolerance.

It is responsibility of the controller to store data to the hard disks.

IT Architecture - Storage Basics-1

IT Architecture

IT architecture describes the way servers and hosts accessing the storage. Storage consists of various disks which are shared between the hosts.

It is deployed in the environment where there is a requirement of shared memory between the server e.g shared drives. Storage disks are appeared as the directly attached disk to the servers.

There are below two types of IT architecture.

1.Server-Centric IT Architecture:-

It is a traditional or legacy design where hosts are accessing storage disk via dedicated servers. They cannot access the storage directly. 

Servers are connected to hosts via traditional LAN and to storage disk via SCSI cables. There is no dedicated storage network for the Hosts

Advantages:-

1. Easy Deployment: - Deployment of server centric IT architecture is simple and easy . It is still in use for small deployments.

2. Less Expensive:- There is no involvement of expensive storage devices and dedicated storage network which saves a lot of expensive. It not only saves the device expense but also the expense on the skill required to deploy and maintain the infrastructure.

Disadvantage:-

1. Less Scalable :- 

•   Each server can support limited number of I/O Cards which restrict the scalable
•   Since SCSI cable has the limitation of 25m length, servers and disk cannot be connected beyond 25m.
•    Storage and servers are deployed locally as per the requirement since it cannot be 25m apart.

2. Less Reliable: - There are usually one or two upfront servers which gives very limited fault tolerance to the design. Failure of server can lead to major outage.

3. Less Efficient: - Suppose Storage disk, i.e. storage-2, connected to server-3 is full, now there is no way for Server-3 to get extra storage even if large amount of space is available on storage-1.

4. Security issues: - Since the deployment is scattered, there are always risk of unauthorized access.

5. Environment issues: - Due to the scattered behavior, it is very difficult of maintain the temperature in the various data closest.

6. Complex design:- It is not suitable for large deployment as it will lead to very complex design.

2.Storage-Centric IT Architecture:-  

IT architecture with storage dedicated network is called storage centric design. All the SCSI cables present in legacy designs are replaced by separated storage network.  Small disk are also replaced by big storage boxes called disk subsystems.

Like server centric design it also has its own advantages and disadvantages which are discussed below.

Advantages:-

1. Efficient: - Now one server can use whatever storage it wants.

2. Scalability- Since there is separate storage network and large storage devices, it is capable of handling large number of hosts. It is highly recommended for large data centers where the number of servers and hosts are high.

3. Secure: - As the storage is located centrally, it is very easy to restrict the unauthorized access.

4.  Environment issues: - Because of less number of data center, it is quite simple to maintain the temperature and monitor other environment parameters.

5.  Simple design:- Storage centric design are quite easy to understand, deploy and maintain.

Disadvantage:-

1. Expensive: - Requirement of separated storage network adds extra cost to the deployment. It also requires storage specific skills to deploy and manage the infrastructure.

2. Suitable for large and medium deployment only.

Cisco 4400 WLC License information

Cisco 4400 series wireless LAN controllers don’t come with software activation option. It means you cannot increase the AP capacity of the controller after the purchase.

There are two models of 4400 series controller

1.4402 series controllers:- It has two gig ports and each port can handle up to 25 Aps. So maximum it can have 50 Aps on 4402.

And hence two 4402 models were supported- 

•   4402-25:- It support maximum 25 APs.
•   4402-50:- It support maximum 50 APs.

2.4404 series controllers: - It has four gigabit port which can support up to 48 AP but only 25 per port are recommended by Cisco.

There were three models available:-

•   4404-25 – Support max 25 APs
•   4404-50 – Support max 50 APs
•   4404-100 – Support max 100 Aps

Note: Cisco 4400 is End of sale now and last date of support is on 16th June 2016.

VPC FAQs

1. Can VPC port-channel number different on peer switch?

Answer: - yes, it can be different

2. Is a single VPC domain between two VDCs on the same physical Cisco Nexus 7000 device supported?

Answer: - No, It is not supported.

3. What are the default parameters of VPC?

Answer:- Below are paramaters.

Parameters	Default
vPC system priority	32667
vPC peer-keepalive interval	1 second
vPC peer-keepalive timeout	5 seconds
vPC peer-keepalive UDP port	3200

4. Are Jumbo frames enabled by default on the vPC peer link.

Answer: Yes, jumbo frame are by default enable.

5. What license is required for VPC?

Answer:- No license is required for VPC

6. Can we create both layer2/3 Only Layer 2 port channels can be in vPCs.

 Answer:- No, we can only configure Layer port-channel in VPC.

7. In VPC peer-link, is F1 on one side and M1 on the peer switch supported?

Answer:- No, Module type of both end should be identical. Please refer to the below table.

vPC Primary	vPC Secondary	Supported/Not supported
F1 I/O module	F1 I/O module	Supported
F1 I/O module	M1 I/O module	Not supported
M1 I/O module	M1 I/O module	Supported
M1 I/O module	F1 I/O module	Not supported

8. Can we use physical interface as VPC peer-link?

Answer: No, VPC peer-link can only be configured on port-channel containing 10 gig interfaces. 1 Gig interfaces  cannot be configured as VPC peer-link

9. Can we configure system-mac for VPC?

Answer: Yes, we can configure the system ID for VPC with below command

Nexus(config)# vpc domain 5

Nexus(config-if)# system-mac 0000.0000.000a

  

10. What is the default role-priority?

Answer: It can be from 1 to 65535 and default value is 32667.

Note: - Lower is better.

11. What is the default VPC domain ID?

Answer: - There is no default domain-id and can be configured from 1 to 1000.

Why we need VPC?

Initially when I heard of VPC, I neither understand the advantage of it nor its difference with VSS. Below I tried to explain the difference between VPC and VSS and the legacy setup where STP is being used to prevent L2 loops. But STP has many limitations which are discussed below:-

1.Suboptimal Path:-  To understand it, take a look to  the below topology where  three switches are connected to provide complete redundant path .

The problem with this design is, STP will block the port Gi0/3 of Sw-2. And hence traffic instead of taking direct route from SW-1 to SW-3, will reach to SW-3 via SW-1 and is known as suboptimal path. It adds extra hop in the path and reduces the efficiency of the network.

 2.Underutilization of uplink bandwidth:-

STP prevents the layer-2 loop by blocking the redundant path which is an advantage but in way reduces the uplink bandwidth which sometimes creates the congestion in the network.

Refer to the below diagram, traffic from SW-3 to internet has two path but due to spanning tree Gig0/3 of SW-3 is in blocking state. It will reduce the uplink bandwidth available to the SW-3.

3.Inefficiency: - Let’s assume the traffic is load share between SW-1 and SW-2 and both switches advertise the user subnet from same metric. There is no problem when the return traffic hit the SW-1 but what will happen when the very first return traffic that hits SW-2.

Does SW-2 have the mac-address of PC-1? Generally NO!

 SW-2 will send the unknown broadcast for the mac-address and if there are many users sitting in the LAN, unknown unicast will not only create the unnecessary traffic but it also impacts the CPU utilization of switches.

By using VSS in 6500, both the switches will virtually become one. One sup is active at a time which will control the data plan of both the chassis. It not remove the layer 2 loop from the network  but also remove the sub-optimal path and inefficiency problem which we had in our legacy environment.

As you can see there is neither a suboptimal path nor there is problem of reduced uplinks. It also removed the unnecessary unknown unicast issue.

But in VSS, control plane is active only on one switch whereas data plane is active on both the switches. As only one Sup is active the overall throughput is limited and other SUP capacity is gone wasted.

Advantage with VPC is not only it removes the above stated problems but also control and data plane of both the chassis are active at the same time. It increases the overall throughput of the system.

In the below design, traffic from PC-1 can directly reach PC-2 with adding any hop.

Also in the below design, traffic from PC-1 can go to internet via SW-1 or SW-2 depending open the hashing algorithm of SW-3. Also it removes the problem of unknown unicast in case of asymmetric routing as both the switch will be appearing as one.

Important port details:- Cisco Wireless

    Important port details:-

        1. Enable these UDP ports for LWAPP traffic:

            Data - 12222
            Control - 12223

        2. Enable these UDP ports for CAPWAP traffic:

            Data - 5247
            Control - 5246

        3. Enable these UDP ports for Mobility traffic:

            16666 - Secured Mode
            16667 - Unsecured Mode

    Mobility and data messages are usually exchanged through EtherIP packets. IP protocol 97 must be allowed on the firewall to allow EtherIP packets. If you use ESP to encapsulate mobility packets, you have to permit ISAKMP through the firewall when you open UDP port 500. You also have to open the IP protocol 50 to allow the encrypted data to pass through the firewall.

    These ports are optional (depending on your requirements):

• TCP 161 and 162 for SNMP (for the Wireless Control System [WCS])
• UDP 69 for TFTP
• TCP 80 and/or 443 for HTTP or HTTPS for GUI access
• TCP 23 and/or 22 for Telnet or secure shell (SSH) for CLI access

OTV FAQs

1.Can OTV VDC configured with SVI of the Extended VLAN?

Answer:-No, OTV VDC cannot have SVI of the extended Vlans.

2.Is OTV supported on all series of line cards?

Answer:- No, OTV is not supported on F1,F2,F2e. It is only supported on M series and F3 line cards.

3.Does OTV advertise the mac-address?

Answer: - Unlike fabricpath, OTV advertise the mac-address.

4.What is the size of OTV header?

Answer: 42 Bytes

5.How the authoritative edge device role is negotiated?

Answer:- Edge device with lower system-id will become authoritative for all even extended vlans and edge devices with higher system-id will be elected for all odd vlans.

6.What is the COS and DSCP value of OTV control packet?

Answer:- COS=6/DSCP=48

7.Can multiple overlay interfaces share the same join interface?

Answer:- Yes, One join interface can be shared between multiple overlay interfaces.

8.How many overlay interfaces can be configured on the edge devices?

Answer:- Maximum 10 overlay interfaces can be configured.

9.How many sites can be paired on OTV?

Answer:- Maximum 6 sites can be configured.

10.   How many edge device per site can exist?

Answer:- Maximum two edge devices can be configured per site.

11. How many vlans can be extended via OTV?

Answer:- Maximum 256 Vlans can be extended.

12.What license is required for OTV?

Answer:- Transport  service license.

13.   Can we configure loopback interface as join interface?

 Answer:- NO, only physical interface, sub-interface,port-channel and port-channel sub interface can be configured as join interface.

SVI and loopback cannot be configured as join interface.

15.Can we configure 1 Gig port as join interface?

Answer:- Yes, there is no restriction for 10 gig.

16. Is OTV support fragmentation?

Answer:- No in OTV fragmentation or reassembly is not supported. All control and data traffic is sent with DF bit sent. OTV adds 42 byte header to IP packet.

17.Is STP BPDU sent across OTV link by default?

Answer: - No, STP BPDU are blocked by default.

18.Is unknown unicast is sent across OTV link?

Answer:- No, it is also not permitted to cross OTV link. OTV assume that there is no silent machine in the environment.