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The Pure Storage Glossary


An individual who administers a FlashArray system. Administrators may be authorized to control an array or may be limited to a monitor role, in which they can observe the array's configuration, state, and performance, but cannot alter its operating parameters.

allocation unit

The unit in which Purity manages flash storage. Each allocation unit consists of several consecutively numbered erase blocks on a flash module. Purity allocates storage in groups of allocation units on different flash modules.

array management port

An Ethernet interface in each FlashArray controller that provides administrative access to the array from browser or virtual terminal-equipped workstations.

back-end controller interconnect network

The dual-path network that interconnects FlashArray controllers.

FlashArray FA-300 and FA-400 series uses InfiniBand ports.

back-end controller interconnect port

A FlashArray back-end controller port used for interconnecting with other controllers in the array.

back-end storage interconnection port

A Serial Attached SCSI (SAS) port in a FlashArray controller or storage shelf used to connect controllers to storage shelves and the flash modules within them.

basic object

A manageable object in a FlashArray system. Basic objects may be hardware (controllers, storage shelves, flash modules, NVRAM modules, front-end ports) or virtual (volumes, hosts, and host groups).

client, client computer

Synonym for host.

client block map

A set of persistent data structures in which Purity maintains the correspondence between volume block addresses exported to hosts and physical storage locations of data.

command line interface (CLI)

The Purity virtual console-based tool used by administrators to monitor and control FlashArray systems. Administrators launch the Purity CLI via a secure shell (ssh) connection (for Windows administrative workstations, typically through a terminal emulator such as PuTTY).

continuous storage reclamation

The Purity process that continually frees lightly occupied allocation units by moving data from them to more densely populated ones. Purity reuses reclaimed allocation units to store host-written data and data consolidated from reclaimed storage.


The FlashArray component that contains a processor complex, DRAM cache, front-end and back-end ports, and an administrative port. The two controllers in a highly-available array cooperate with each other to provide a failure tolerant, high-performing, single-image storage system.

controller pair

Synonym for partner controllers.

data reduction

Reduction in the size of a set of data by elimination of duplication. Purity reduces blocks of data written by hosts by eliminating repeating patterns, deduplicating entire blocks against each other, and compressing non-duplicate blocks, continuously throughout their lives in an array.

disk block

Synonym for sector. The atomic unit in which magnetic disk drives read, write, and ECC-protect data. Analogous to a flash page in a flash module.

eradication pending state

A state in which an administrator places a volume by executing a purevol destroy command against it. Purity does not export volumes in the eradication pending state; they are invisible to most administrative operations. Volumes remain in the eradication pending state for 24 hours, after which Purity eradicates them, deleting their data and freeing the storage capacity they occupy.

erase block

The unit of memory in which flash memory erases data prior to overwriting. Each erase block consists of multiple consecutively addressed flash pages.


(v.) To present one or more objects to clients. A FlashArray system exports disk-like volumes to its clients (host computers).

Fibre Channel front-end port

A FlashArray controller front-end port that implements Fibre Channel physical signaling and low-level protocol.

flash module

A data storage device based on a persistent flash technology. Solid-state drives are the physical data storage elements in FlashArray systems.

flash page

The atomic unit in which data is read from flash memory.


A scalable enterprise-class high-performance data storage system based entirely on flash storage technology.

front-end host connection port

A FlashArray controller port used to connect host(s) to the array, usually via a storage network. Host connection ports implement either the Fibre Channel Protocol or the iSCSI protocol.

graphical user interface (GUI)

A user interface to a computer that represents objects and methods graphically rather than with character strings. The Purity GUI runs within the context of a browser.

group object

A Purity construct for managing collections of basic objects (hosts and volumes). Administrators can create group objects for management convenience, particularly in arrays that support large numbers of volumes.

high availability

The ability of a system to sustain a major component failure and continue to perform its function. Typically achieved by configuring and integrating redundant components and connections and implementing software that detects and isolates failures, “heals” the functions they affect, and assists in repair, replacement, and reassimilation of components.


A server or desktop computer connected to a FlashArray system via a storage network that makes use of the array's data storage services. Hosts may be physical or virtual, and are identified to Purity by the port names used to connect them to the FlashArray system.

host capacity

Synonym for size (q.v.).

host occupancy

The amount of host-visible storage occupied by host-written data: the number of unique volume sector addresses written by hosts (and not trimmed) multiplied by the size of a sector (512 bytes).

host port (H-port)

An I/O port in a host used to connect to a FlashArray system, usually via a storage network.

host-written data

Data written by a host to one or more volume sector addresses in a FlashArray volume.

InfiniBand (IB)

An interconnect standard created by server manufacturers. Used primarily to connect servers at high speeds over short distances. The FlashArray FA-300 and FA-400 series use InfiniBand to interconnect a highly-available array’s controllers. FlashArray//m uses InfiniBand ports for upgrades.

initial data reduction

Purity’s first-pass reduction of data as it enters an array. Initial data reduction includes elimination of patterned blocks and may also include deduplication and compression of non-duplicates.


A device that provides dual-channel access to a flash module and also converts between the SATA protocol native to FlashArray flash modules and the SAS protocol used to communicate with controllers. Interposers are mounted in the storage carriers that hold flash modules.

I/O card

A PCI Express interface module in a FlashArray controller containing either SAS ports that connect to storage shelves, InfiniBand or NTB ports used to interconnect controllers, or Fibre Channel or iSCSI ports that provide access to the external environment.

The FlashArray FA-300 and FA-400 series use InfiniBand ports.

I/O module

A FlashArray storage shelf component containing a SAS expander that fans out an incoming SAS bus to the flash modules and NVRAM modules within the shelf and to other shelves downstream from it. Each storage shelf contains two I/O modules, providing redundant access paths to the flash modules and NVRAM modules within it.

I/O performance density

The number of I/O operations per second of which a storage system is capable divided by the effective data storage capacity of the system. For example, a storage system that presents 10 terabytes of usable storage and is capable of 100,000 IOPS has an I/O performance density of 10,000 IOPS per terabyte.

I/O port

A connection point (socket) on an I/O card. I/O ports interconnect array components, and provide access to the external environment for I/O. The I/O ports in storage shelves are SAS ports. Those in controllers are back-end SAS, InfiniBand ports, or Fibre Channel or iSCSI front-end ports.


I/O operations per second. The preferred measure of I/O performance with random (non-sequential) I/O workloads.

logical block

Synonym for sector.

logical block address (LBA)

The mechanism by which logical blocks are addressed in read and write commands to disk drives and flash modules.

logical block number (LBN)

Synonym for logical block address.

logical page

The atomic unit in which Purity reads data from flash modules. Consists of one or more flash pages in which data and metadata are stored. Purity computes and stores a checksum in each logical page, and recalculates it when the page is read to detect read errors that are not discovered by flash devices' mechanisms.

logical page checksum

A checksum that Purity calculates and appends to each logical page it writes for the purpose of detecting read errors that are not detected by flash devices' ECC mechanisms.

logical unit

Synonym for volume.

logical unit number (LUN)

The mechanism for addressing a logical unit or volume.

management port (M-port)

A FlashArray controller port used for connecting a management workstation to the array, usually via a data center network.


Purity's advanced implementation of thin provisioning, in which only the storage required to contain reduced data blocks and the metadata that describes them is allocated.

non-volatile random access memory (NVRAM)

Randomly addressable memory whose contents survive power outages intact. FlashArray controllers store host-written data temporarily in NVRAMs mounted in storage shelves prior to writing it to flash modules, so that power outages and system resets do not result in data loss.

object database

A persistent database used internally by Purity to maintain records related to both the intrinsic and administrator-defined virtual objects in an array.


A measure of the physical or host-visible storage occupied by host-written data.


In this guide, a synonym for flash page (q.v.).

partner controllers

Two Pure Storage controllers connected to the same (two or more) storage shelves. Partner controllers maintain synchronized copies of each others’ NVRAM contents so that if one of them should fail, its partner can control all flash modules and export volumes seamlessly to hosts on its front-end host connection ports.

patterned block

A block of data received from a host whose contents consist of a repeated data pattern of between 1 and 8 bytes. Purity does not allocate storage for patterned block data, but records their existence in its internal metadata.

physical occupancy

The amount of physical storage occupied by host-written data after reduction by Purity.


An interface between FlashArray components (controllers and storage shelves), or between controllers and a network or host. Array controllers contain front-end ports for connecting to hosts via storage networks, back-end ports that interconnect the controllers in a highly available array, back-end SAS ports that connect controllers to storage shelves, and GbE administrative ports that connect controllers to a network for administration. Storage shelves contain SAS ports that connect to controllers and interconnect storage shelves with each other.

Purity CLI

The CLI used to administer a FlashArray system. The Purity CLI runs on an array and is accessed via a virtual terminal emulator such as PuTTY.

Purity GUI

The browser-based graphical user interface used to administer FlashArray systems.

Purity Operating Environment (Purity)

The operating system and array logic that run in each FlashArray controller.


FlashArray’s dynamic multi-level scheme for protecting against data loss due to uncorrectable read errors and device failures. RAID-3D minimizes the impact of read error recovery, and automatically adjusts protection parameters based on the nature of stored data and conditions within an array.


Synonym for data reduction.

reduction ratio

Any of several ratios of the amount of physical storage occupied by data and the data’s host-visible size.


The common 512-byte unit in which data is written to, read from, and ECC-protected on disk drives and flash modules. Pure Storage volumes present virtual sectors of storage in which hosts can read and write data.


A Purity data structure consisting of groups of allocation units, each on a separate flash module. The segment is the unit in which Purity allocates storage capacity for writing data and metadata, as well as the unit of RAID protection. Purity assigns each segment’s RAID protection scheme at allocation time.

Serial-Attached SCSI (SAS)

The industry standard technology that connects storage shelves (and the flash modules within them) to controllers in FlashArray systems.


The storage capacity of a volume as it appears to hosts' storage administration tools.


A host-accessible virtual image of the contents of a set of data as they appeared at some point in time. Purity snapshots capture virtual images of volume contents, and appear to hosts as read-only volumes.

storage area network (SAN), storage network

A network whose primary purpose is to enable communication between hosts and storage devices or systems. FlashArray systems support Fibre Channel and iSCSI storage networks.

storage shelf

The FlashArray component that houses flash modules. In a highly available array, each storage shelf connects to a pair of controllers to provide redundant access and performance scaling.

thin provisioning

A storage virtualization technique in which allocation of physical storage to volume blocks is deferred until a host writes data to the volumes' block addresses.


(v.) Deallocation of storage capacity that holds host-written blocks that a host has indicated are no longer in use (via a SCSI trim command).

virtual space

The amount of virtual space in a volume or array that is occupied by host-written data.


A disk-like random access virtual storage device that a FlashArray system exports to hosts via a logical unit number (LUN). To a host, a FlashArray volume contains a number of 512-byte sectors in which data can be written and from which it can be read.

write amplification

The generation of additional I/O internal to a conventional array or flash storage as a consequence of a single write request. A write to a RAID group in an array that is smaller than the group's data stripe size results in one or more internally generated log-read-modify-write sequences in order to synchronize RAID check data. A write to a flash module may require block erasure, resulting in a read of an erase block to preserve existing data, a block erasure, and an overwrite of the block with a combination of new and existing data. Write amplification is functionally invisible to the writer, but takes time and consumes internal bandwidth.

write buffer

A DRAM buffer in which Purity stages data for writing to persistent flash module storage. The size of a write buffer is the same as that of a write stripe unit. Purity writes all buffers in a write stripe in sequence.