1. Agenda CS C446 Data Storage Technologies & Networks
Storage Area Networks
Structure and Architecture
Addressing
Zoning, Trunking and Multipathing

2. Storage Area Networks Storage units are on the network
Network is (typically) different from the LAN
Fibre-Channel SAN
Data is accessed raw (in disk blocks) from storage units
As opposed to file access in NAS
Fibre-Channel SANs were the earliest:
FC offers high Bandwidth
Alternative SAN technologies available today:
E.g. IP SAN
SAN and NAS are converging:
E.g. NAS head with a SAN backend.
Sundar B.

3. SAN - Purpose Primary purpose Non-functional requirements
Aggregation of physical storage devices permitting logical, on-the-fly division/sharing among hosts
Non-functional requirements
High transfer rates
High availability
Sundar B.

4. SAN Components and Structure
Hosts (client / server computers)
Storage Devices
Interfaces (ports for communication)
Hubs, Switches, and Gateways
Structure - Example
Storage devices thru’ ports are connected to an (FC) AL hub:
Local hosts are also connected to the AL via I/O bus adapters and ports
Hubs do not allow high transfer rate (due to sharing) but are cheap.
The hub is connected through a FC-switch to remote hosts (referred to as switched fabric)
Switches allow individual connections with high transfer rates but are expensive.
Gateways enable connection of SAN over WANs
SAN to SAN
SAN to hosts on the Internet
Sundar B.

5. SAN Components and Structure
Interconnects
Cables – Fiber Optic Serial
Transceivers,
Interface Converters (Optical/Electrical),
Host-Bus Adapters (Parallel-Serial Conversion)
Inter Switch Links (connect E-ports)
Cascading
Seamless extension of fabric by adding switches
Interswitch links can also provide redundant paths
Devices
Hubs, Switched Hubs, Switches/Directors
Multiprotocol Routers (FCP, FCIP, iFCP, IP iSCSI)
Sundar B.

6. SAN – Addressing WWN unique World Wide Name per N-port
Devices may have a WWN (independent of the adapters/ports)
Defined and maintained by IEEE
64-bit long
24-bit port addresses may be used locally to reduce overhead.
Sundar B.

7. SAN – Addressing 24-bit addressing - in a switched fabric
Assigned by switch
At login, each WWN is assigned (mapped) to a 24-bit address by Simple Name Service (SNS)
SNS is a component of the fabric OS – acts as a registry/database
Address format:
domain address (bits 23-16) identifies the switch
Some addresses are reserved e.g broadcast;
239 possible addrs.
area address (bits 15-8) identifies a group of F-ports,
port address (bits 7-0) identifies a specific N-port
Total addressible ports: 239x256x256
Sundar B.

8. SAN – Addressing 24-bit addressing - in an AL
Obtained at loop initiation time and
re-assigned at login to the switch
Address Format:
Fabric loop address (bits 23-8) identifies the loop
All 0s denotes a private loop i.e., not connected to any fabric
Port address (bits 7-0) identifies a specific NL-port
Only 126 addresses are usable (for NL-ports):
8B/10B encoding is used for signal balancing;
Out of the 256 bit patterns only 134 have neutral running disparity – 7 are reserved for FC protocol usage; 1 for an FL-port (so that the loop can be on the fabric);
Sundar B.

9. SAN – Routing Routing Analogous to switching in a LAN Goal:
Keep a single path (bet. Any two ports) alive – no redundant paths or loops
Additional paths are held in reserve – may be used in case of failures.
Fabric Shortest Path First (FSPF) protocol –
Cost: hop count
Link state protocol
Link state database (or topology database) kept in switches
Updated/Initialized when switch is turned on or new ISL comes up or an ISL fails
Switches use additional logic when hop count is same.
Round Robin is often used for load sharing
Sundar B.

10. SAN - Zoning Zoning allows fabric segmentation:
Storage (traffic) isolation
E.g. Scenario: Windows systems claim all visible storage
Hardware Zoning: (1-1, 1-*, *-*)
Based on ports connected to fabric switches (switches-internal port numbering is used)
A port may belong to multiple zones
Adv: Implemented into a routing engine by filtering
Disadv: Device connections are tied to (physical) ports
Software Zoning:
Based on WWN – managed by the OS in the switch
Less secure due to spoofing possibilities
Sundar B.

11. SAN - Zoning Software Zoning:
Based on WWN – managed by the OS in the switch
Number of members in a zone limited by memory available
A node may belong to more than one zone.
More than one sets of zones can be defined in a switch but only set is active at a time
Zone sets can be changed without bringing switch down
Less secure :
SZ is implemented using SNS
Device may connect directly to switch without going through SNS
WWN spoofing
WWN numbers can be probed
Sundar B.

12. SAN – Frame Filtering Frame Filtering
Process of inspecting each frame (header info.) at hardware level for access control purposes
Usually implemented as an ASIC w/ choice and configuration of filter that can be done at switch initialization/boot time.
Allows zoning to be implemented with access control performed at wire speed
Port level Zoning, WWN level Zoning, Device level Zoning, LUN level Zoning, and Protocol level Zoning can be implemented using Frame Filtering
Sundar B.

13. SAN – Trunking Trunking
Grouping of ISLs into a trunk i.e. a logical link
Useful for load sharing in the presence of zoning
i.e. zoning need not restrict ISL usage
Supports in-order end-to-end
Re-ordering done by the switch as required
Sundar B.

14. SAN – Multipathing Multipathing
Provide multiple paths between a host and a device (LUN).
Redundancy for improved reliability and/or higher bandwidth for improved availability / performance
Channel subsystem of the kernel in switch OS handles multipathing at software level
Usually Separate device driver is used w/ following capabilities:
Enhanced Data Availability
Automatic path failover and recovery to alternative path
Dynamic Load balancing
Path selection policies
Failures handled:
Device Bus adapters, External SCSI cables, fibre connection cable, host interface adapters
Additional software needed for ensuring the host sees a single device.
Sundar B.

15. SAN - LUN Masking
Zoning imposes some logical traffic isolation as well as some access control of devices.
Alternative – LUN Masking:
Storage Device Control program (part of the switch OS) maintains an access lists for the storage device
One list per LUN
When hosts require access they request access to a LUN and the device control program verifies the list before granting access
Sundar B.

16. Storage Virtualization
Integration of back-end devices and functions with front end functionality to provide certain abstractions.
Different levels:
Device Level
Physical devices are collected and presented as different virtual devices (e.g. partitions, RAID array controllers etc.)
File System Level
Block storage devices are presented as file systems
Fabric Level
Virtual Devices and collections are aggregated and presented as storage groups with high level access control (e.g. Zoning)
Server Level
Servers interpret the available storage as different units as per the requirement (Logical Volume Management at the host OS level)
Sundar B.

17. Storage Virtualization
In-band implementation
Data and control flow thru’ same lines
Easy to implement
Homogeneous environment (even with heterogenous devices)
Scalable
Out-of-band implementation
Control flows through separate lines
Separate server(s) maintain metadata
Metadata: mapping tables, locking tables, access control
Server Known as metadata controller
Authentication needed for hosts
Add-on flexibility
E.g. Adding a file server / file system on a SAN environment
High Bandwidth availability for data traffic
Sundar B.

18. Emerging Protocols
iSCSI
iFCP
FCIP – FC tunnelling
Sundar B.