The difference between unmanaged and managed switches.

http://www.cisco.com/en/US/prod/switches/networking_solutions_products_genericcontent0900aecd806c7afe.pdf

Managed Switch :

Managed switches give you more control over your LAN traffic and offer
advanced features to control that traffic.

An unmanaged switch simply allows Ethernet devices to communicate with one another, such as a
PC or network printer, and those are typically what we call “plug and play.” They are shipped with a
fixed configuration and do not allow any changes to this configuration.

An unmanaged switch allows devices to talk to each other, but that is pretty much all
that they do?

Managed switches provide all the features of an unmanaged switch and provide the
ability to configure, manage, and monitor your LAN. And this gives you greater control over how
data travels over the network and who has access to it.

Also, managed switches use protocols such as the Simple Network Management Protocol, or what
we call SNMP, for monitoring the devices on the network. SNMP is a protocol that facilitates the
exchange of management information between network devices. SNMP queries can determine the
health of the network or the status of a particular device. By displaying this data in an easily
understood format, IT managers located at a central site can monitor the performance of the
network and quickly detect and repair network problems without having to physically interact with
the switch.

So SNMP allows me to remotely monitor my network devices, and I don’t have to
go to the site to make changes or troubleshoot the switch?

Ok, let’s talk about costs. I understand that managed switches are more expensive than
unmanaged switches. Why should one pay more for a managed switch?
It’s true that a managed switch is more expensive than an unmanaged switch. However,
there are many additional features you get with a managed switch, such as quality of service,
virtual LANs, redundancy, and port mirroring.

These features help provide control over the traffic traveling over the switch.
Maybe we can take a few minutes to go through each of these features and their benefits so you
can get a better understanding of them.

All right, then, we’ll start with quality of service. Quality of service allows you to prioritize
your network traffic by assigning a higher priority to critical traffic. This helps ensure consistent
network performance and can support delay-sensitive data such as real-time voice. For instance, if
I know I have voice packets traveling over my network, I want to make sure they have the highest
priority so that these voice packets don’t get dropped or delayed and mangle the phone
conversation.
I know what you’re talking about. It’s so frustrating to miss half of what a caller is
saying. What about virtual LANs, VLANs?

VLANs allow a switch to logically group devices together to isolate traffic between these
groups even when the traffic is passing over the same physical switch. This segmentation and
isolation of network traffic help reduce unnecessary traffic. For instance, you can segment traffic
between your finance and marketing groups, so that mission-critical finance information can flow
without delay to the finance users and get bogged down by marketing traffic. This allows better
network performance and in many cases provides an additional level of security.
Another important feature of a managed switch is redundancy. Redundancy provides the ability to
safeguard a network in case a connection or cable fails by providing an alternate data path for
traffic. Managed switches incorporate what is called Spanning Tree Protocol standard, or STP, to
provide path redundancy in the network. Using the spanning-tree algorithm, STP provides
redundant paths while preventing loops that are created by multiple active paths between switches.
STP allows for one active path at a time between two network devices, preventing loops and
establishing the redundant links as a backup to keep integrated systems available and preventing
expensive downtime, which network admins can appreciate.
And, finally, there is port mirroring. In conjunction with a network analyzer, this feature is useful to
diagnose problems. It copies the switch network traffic and forwards it to a single port on the same
switch for analysis by a network analyzer. You can use the analyzer on a monitor port to
troubleshoot network problems by examining traffic on other ports or segments. The benefit of this
is you can troubleshoot problems without taking the network out of service

I can see how they can improve network
performance and give users a more consistent experience with their network.
But why should someone consider using a managed switch?

Each business needs to evaluate the needs of their network. When their network
requirements have evolved to the point where they would like to have some input and control over
the behavior of traffic on their LAN, then it is a good time to consider a managed switch. Also, if you
are planning to deploy advanced services such as wireless LANs or IP telephony in the near future,
managed switches can lay the foundation for these technologies.



Some of the uls may be useful :

http://www.cisco.com/go/switching.
http://www.cisco.com/go/switching

Raid 0+1

RAID 0+1
Provides redundancy by writing all data to four or more drives.RAID 0+1 combines the benefits of RAID level 0 and RAID level 1.This offers both striping and mirroring with no parity generation.The RAID 0+1 also provides high performance and resilience to RAID 5.


Advantages
No parity generation
Easy to implement
Utilises full disk capacity
4 drives minimum
Higher performance than RAID 5
Disadvantages
Inefficient use of disk space
High disk overhead / Expensive
Costly to deploy

Applications
General File servers
Imaging applications
Medium size database applications

Raid 10

RAID 10
Provides very high performance and redundancy. Datais simultaneously mirrored and striped. Can under circumstancessupport multiple drive failures.


Advantages
Highly fault tolerant
High data availability
Very good read / write performance
Disadvantages
Very expensive
Drive spindles must be synchronised
Not very scaleable

Applications
Where high performance and redundancy are critical

Raid 5

RAID 5
Provides redundancy by writing data and parity informationacross three or more drives, thus increasing performance. The RAID Level 5provides the best combination of disk array technology. The mostpopular RAID level supplied.


Advantages
Most flexible of all disk arrays
Best balance cost / performance / protection of any RAID system
Allows multiple simultaneous writes
High read data rate
Medium write data rate
3 drives minimum
Ideal for small write applications
Highly efficient
Disadvantages
Inefficient with large file transfer
Disk failure has an impact on performance

Applications
Transaction processing
Relational Databases
File & Print Servers
WWW, E-mail, and News servers
Intranet Servers

Raid 3

RAID 3
Provides redundancy by writing all data to three or moredrives. This RAID 3 disk array provides excellent storage for videoimaging, streaming, publishing applications or any system that requireslarge file block transfers.


Advantages
Single dedicated parity disk
High read data rate
High write data rate
4 drives minimum
No performance degradation if drive fails
Best and worst case performance similar
Disadvantages
Inefficient with small file transfer

Applications
Video Streaming
Video Publishing
Video Editing
Pre Press
Image editing
Any application that needs heavy updating and large file usage

RAID 1
Provides redundancy by writing all data to two or more drives.The performance of a level 1 array tends to be faster on reads andslower on writes compared to a single drive, but if either drive fails,no data is lost. This is a good entry-level redundant system, since onlytwo drives are required; however, since one drive is used to store aduplicate of the data, the cost per megabyte is high. This level iscommonly referred to as mirroring.


Advantages
No parity generation
Easy to implement
Extremely fault tolerant
Utilises full disk capacity
2 drives minimum
Disadvantages
Inefficient use of disk space
High disk overhead
Doubles number of writes

Applications
Pre-Press
Video editing and production
Image manipulation/editing

Raid 0

Top Raid 0 Raid 1 Raid 3 Raid 5 Raid 10 Raid 0+1


RAID 0
Offers no redundancy or fault tolerance, hence does not truly fit the"RAID" acronym. In level 0, data is striped across drives,resulting in higher data throughput. Since no redundant information isstored, performance is very good, but the failure of any disk in thearray results in data loss. This level is commonly referred to asstriping.


Advantages
No parity generation
Easy to implement
Cost effective
Utilises full disk capacity
Disadvantages
Not a true RAID
No redundancy / fault tolerance
Drive failure will result in data loss
Not suitable in mission critical environments

Applications
Pre-Press
Video editing and production
Image manipulation/editing


Dual controller Raid 0 offers better performance than a single controller