Persistent binding

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Host-based zoning can include WWN or LUN masking, and is typically known as “persistent binding.”

A World Wide Name (WWN) or World Wide Identifier (WWID) is a unique identifier used in storage technologies including Fibre Channel, Advanced Technology Attachment (ATA) or Serial Attached SCSI (SAS).

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In storage networking, ”persistent binding” is an option of zoning.

In storage networking, Fibre Channel zoning is the partitioning of a Fibre Channel fabric into smaller subsets to restrict interference, add security, and to simplify management. While a SAN makes available several devices and/or ports to a single device, each system connected to the SAN should only be allowed access to a controlled subset of these devices/ports. Zoning applies only to the switched fabric topology (FC-SW), it does not exist in simpler Fibre Channel topologies.

Host-based zoning is usually referred to as persistent binding or LUN, [1] and is perhaps the least implemented form of zoning. Because it requires the host configuration to be correct in order to avoid zoning conflicts, this form of zoning creates a greater opportunity for administrative errors and conflicting access to targets. Moreover, zoning interfaces vary among different host operating systems and HBA's — increasing the possibility for administrative errors. If a host is not configured with the zoning software, it can access all devices in the fabric and create an even higher probability of data corruption. Host-based zoning is often used when clusters are implemented to control the mapping of devices to specific [2] target IDs. However, it should never be the only form of zoning. Augmenting host-based zoning with storage- and fabric-based zoning is the only acceptable method to reliably control device access and data security.

Operating system collection of software that manages computer hardware resources

An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs.

Host adapter device which connects a computer, which acts as the host system, to other network and storage devices

In computer hardware, a host controller, host adapter, or host bus adapter (HBA) connects a computer, which acts as the host system, to other network and storage devices. The terms are primarily used to refer to devices for connecting SCSI, Fibre Channel and SATA devices. Devices for connecting to IDE, Ethernet, FireWire, USB and other systems may also be called host adapters.

Data security means protecting digital data, such as those in a database, from destructive forces and from the unwanted actions of unauthorized users, such as a cyberattack or a data breach.

Basically, A given LUN has it SCSI id assigned by its RAID device (typically a SAN ). But for some purposes it's useful to have the SCSI id assigned by the host itself: that's persistent binding.

SCSI set of standards for physically connecting and transferring data between computers and peripheral devices

Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interfaces. SCSI is most commonly used for hard disk drives and tape drives, but it can connect a wide range of other devices, including scanners and CD drives, although not all controllers can handle all devices. The SCSI standard defines command sets for specific peripheral device types; the presence of "unknown" as one of these types means that in theory it can be used as an interface to almost any device, but the standard is highly pragmatic and addressed toward commercial requirements.

A disk array controller is a device which manages the physical disk drives and presents them to the computer as logical units. It almost always implements hardware RAID, thus it is sometimes referred to as RAID controller. It also often provides additional disk cache.

Storage area network network which provides access to consolidated, block level data storage

A storage area network (SAN) or storage network is a Computer network which provides access to consolidated, block-level data storage. SANs are primarily used to enhance accessibility of storage devices, such as disk arrays and tape libraries, to servers so that the devices appear to the operating system as locally-attached devices. A SAN typically is a dedicated network of storage devices not accessible through the local area network (LAN) by other devices, thereby preventing interference of LAN traffic in data transfer.

What is Persistent binding for ?

Without persistent binding, after every reboot, the SCSI id of a LUN may change. For Example, under Linux, a LUN bound on /dev/sda could migrate to /dev/sdb after a reboot. The risks augments with multipathing. Based on that, it is obvious that many software may crash without persistent binding.

Linux Family of free and open-source software operating systems based on the Linux kernel

Linux is a family of free and open-source software operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution.

Multipath I/O

In computer storage, multipath I/O is a fault-tolerance and performance-enhancement technique that defines more than one physical path between the CPU in a computer system and its mass-storage devices through the buses, controllers, switches, and bridge devices connecting them.

from http://www.storagesearch.com/datalink-art1.html

Operating systems and upper-level applications (such as backup software) typically require a static or predictable SCSI target ID for their storage reliability and persistent binding affords that happening.

Types of zoning

A zone can include host and LUNS. The LUNS are exported by the DISK ARRAY, the hosts are the clients (servers, computers). Each host in a zone can access each LUNS in the same zone. That's zoning. The zone is usually set on the central point of connection of the hosts and the DISK ARRAY: the FC switch.

LUN masking

from Fibre Channel zoning

Zoning is sometimes confused with LUN masking, because it serves the same goals. LUN masking, however, works on Fibre channel level 4 (i.e. on SCSI level), while zoning works on level 2. This allows zoning to be implemented on switches, whereas LUN masking is performed on endpoint devices - host adapters or disk array controllers.

Some fibre channel switches allow zoning at the LUN level, effectively implementing LUN masking at the switch.

Here, we are talking about level 4.

This form of zoning has to be augmented by another zoning : RAID ARRAY based or fabric-based(FC switch) to improve security and avoid any errors. Otherwise two hosts may access the same data(LUNS) at the same time and it will result in data corruption. Persistent binding is often used in a cluster environment, to associate a LUN with a persistent SCSI id and device (example /dev/sda)

Related Research Articles

In computing, iSCSI is an acronym for Internet Small Computer Systems Interface, an Internet Protocol (IP)-based storage networking standard for linking data storage facilities. It provides block-level access to storage devices by carrying SCSI commands over a TCP/IP network. iSCSI is used to facilitate data transfers over intranets and to manage storage over long distances. It can be used to transmit data over local area networks (LANs), wide area networks (WANs), or the Internet and can enable location-independent data storage and retrieval.

The disk controller is the controller circuit which enables the CPU to communicate with a hard disk, floppy disk or other kind of disk drive. Also it provides an interface between the disk drive and the bus connecting it to the rest of the system.

Clariion

Clariion is a discontinued SAN disk array manufactured and sold by EMC Corporation, it occupied the entry-level and mid-range of EMC's SAN disk array products. In 2011, EMC introduced the EMC VNX Series, designed to replace both the Clariion and Celerra products.

In computer storage, a logical unit number, or LUN, is a number used to identify a logical unit, which is a device addressed by the SCSI protocol or Storage Area Network protocols which encapsulate SCSI, such as Fibre Channel or iSCSI.

ATA over Ethernet (AoE) is a network protocol developed by the Brantley Coile Company, designed for simple, high-performance access of block storage devices over Ethernet networks. It is used to build storage area networks (SANs) with low-cost, standard technologies.

Logical Unit Number Masking or LUN masking is an authorization process that makes a Logical Unit Number available to some hosts and unavailable to other hosts.

In Fibre Channel protocol, a registered state change notification (RSCN) is a Fibre Channel fabric's notification sent to all specified nodes in case of any major fabric changes. This allows nodes to immediately gain knowledge about the fabric and react accordingly.

Is a computer storage product by NetApp running ONTAP operation system; terms ONTAP, AFF, FAS often used as synonyms, also filer is a synonyms though it is not an official name. There are two types of FAS systems, Hybrid and All-Flash:

  1. NetApp proprietary custom-build hardware appliances with HDD or SSD drives called hybrid Fabric-Attached Storage
  2. NetApp proprietary custom-build hardware appliances with only SSD drives and optimized ONTAP for low latency called ALL-Flash FAS.

The IBM SAN Volume Controller (SVC) is a block storage virtualization appliance that belongs to the IBM System Storage product family. SVC implements an indirection, or "virtualization", layer in a Fibre Channel storage area network (SAN).

Internet Fibre Channel Protocol (iFCP) is a gateway-to-gateway network protocol standard that provides Fibre Channel fabric functionality to Fibre Channel devices over an IP network. It is officially ratified by the Internet Engineering Task Force. Its most common forms are in 1 Gbit/s, 2 Gbit/s, 4 Gbit/s, 8 Gbit/s, and 10 Gbit/s.

In computer science, storage virtualization is "the process of presenting a logical view of the physical storage resources to" a host computer system, "treating all storage media in the enterprise as a single pool of storage."

LIO (SCSI target)

In computing, Linux-IO (LIO) Target is an open-source implementation of the SCSI target that has become the standard one included in the Linux kernel. Internally, LIO does not initiate sessions, but instead provides one or more Logical Unit Numbers (LUNs), waits for SCSI commands from a SCSI initiator, and performs required input/output data transfers. LIO supports common storage fabrics, including FCoE, Fibre Channel, IEEE 1394, iSCSI, iSCSI Extensions for RDMA (iSER), SCSI RDMA Protocol (SRP) and USB. It is included in most Linux distributions; native support for LIO in QEMU/KVM, libvirt, and OpenStack makes LIO also a storage option for cloud deployments.

SCST

SCST is a GPL licensed SCSI target software stack. The design goals of this software stack are high performance, high reliability, strict conformance to existing SCSI standards, being easy to extend and easy to use. SCST does not only support multiple SCSI protocols but also supports multiple local storage interfaces and also storage drivers implemented in user-space via the scst_user driver.

References

  1. mapping
  2. SCSI