Agenda

1. CS C446 Data Storage Technologies & Networks Agenda 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 • 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 • Components • 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 • 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.