Glossary

This glossary defines the terms used in this document.


access policy		A volume property indicating what kind of access is allowed for a particular volume. The possible values are Read/Write, Read Only, or Blocked.
array		A group of drives attached to a RAID controller on which one or more volumes can be created. All volumes in the array use all of the drives in the array.
BIOS		Basic Input/Output System. The computer BIOS is stored on a flash memory chip. The BIOS controls communications between the microprocessor and peripheral devices, such as the keyboard and the video controller, and miscellaneous functions, such as system messages.
cache		Fast memory that holds recently accessed data. Use of cache memory speeds subsequent access to the same data. When data is read from or written to main memory, a copy is also saved in cache memory with the associated main memory address. The cache memory software monitors the addresses of subsequent reads to see if the required data is already stored in cache memory. If it is already in cache memory (a cache hit), it is read from cache memory immediately and the main memory read is aborted (or not started). If the data is not cached (a cache miss), it is fetched from main memory and saved in cache memory.
caching		The process of using a high speed memory buffer to speed up a computer system’s overall read/write performance. The cache can be accessed at a higher speed than a drive subsystem. To improve read performance, the cache usually contains the most recently accessed data, as well as data from adjacent drive sectors. To improve write performance, the cache can temporarily store data in accordance with its write back policies.
capacity		A property that indicates the amount of storage space on a drive or volume.
coerced capacity		A drive property indicating the capacity to which a drive has been coerced (forced) to make it compatible with other drives that are nominally the same capacity. For example, a 4-GB drive from one manufacturer might be 4196 MB, and a 4-GB from another manufacturer might be 4128 MB. These drives could be coerced to a usable capacity of 4088 MB each for use in a array in a storage configuration.
coercion mode		A controller property indicating the capacity to which drives of nominally identical capacity are coerced (forced) to make them usable in a storage configuration.
consistency check		An operation that verifies that all stripes in a volume with a redundant RAID level are consistent and that automatically fixes any errors. For RAID 1 arrays, this operation verifies correct mirrored data for each stripe.
consistency check rate		The rate at which consistency check operations are run on a computer system.
controller		A chip that controls the transfer of data between the microprocessor and memory or between the microprocessor and a peripheral device such as a drive. HPE Smart Array P824i-p MR Gen10 Controllers perform RAID functions such as striping and mirroring to provide data protection.
copyback		The procedure used to copy data from a source drive of a volume to a destination drive that is not a part of the volume. The copyback operation is often used to create or restore a specific physical configuration for a array (for example, a specific arrangement of array members on the device I/O buses). The copyback operation can be run automatically or manually. Typically, a drive fails or is expected to fail, and the data is rebuilt on a spare drive. The failed drive is replaced with a new drive. Then the data is copied from the spare drive to the new drive, and the spare drive reverts from a rebuild drive to its original spare drive status. The copyback operation runs as a background activity, and the volume is still available online to the host.
current write policy		A volume property that indicates whether the volume currently supports Write Back mode or Write Through mode. In Write Back mode, the controller sends a data transfer completion signal to the host when the controller cache has received all of the data in a transaction. In Write Through mode, the controller sends a data transfer completion signal to the host when the drive subsystem has received all of the data in a transaction.
device ID		A controller or drive property indicating the manufacturer-assigned device ID.
DDF		Data disk format.
drive type		A drive property indicating the characteristics of the drive.
fast initialization		A mode of initialization that quickly writes zeros to the first and last sectors of the volume. This allows you to immediately start writing data to the volume while the initialization is running in the background.
fault tolerance		The capability of the drive subsystem to undergo a single drive failure per array without compromising data integrity and processing capability. HPE Smart Array MR Controllers provide fault tolerance through redundant arrays in RAID levels 1, 5, 6, 10, 50, and 60. They also support spare drive drives and the auto-rebuild feature.
firmware		Software stored in read-only memory (ROM) or programmable ROM (PROM). Firmware is often responsible for the behavior of a system when it is first turned on. A typical example would be a monitor program in a system that loads the full operating system from a drive or from a network, then passes control to the operating system.
formatting		The process of writing a specific value to all data fields on a drive, to map out unreadable or bad sectors. Because most drives are formatted when manufactured, formatting is usually done only if a drive generates many media errors.
FS		File system.
GUI		Graphical user interface.
HPE Smart Storage Energy Pack		Refers to a energy pack backup unit.
JBOD		Just a bunch of disks. JBOD generally refers to a collection of hard disks that are directly managed by the host. JBOD is an alternative to using a RAID configuration. Rather than configuring a storage array to use a RAID level, the disks within the array are treated as independent disks.
initialization		The process of writing zeros to the data fields of a volume and, in fault-tolerant RAID levels, generating the corresponding parity to put the volume in a Ready state. Initialization erases all previous data on the drives. Arrays will work without initializing, but they can fail a consistency check because the parity fields have not been generated.
IO policy		A volume property indicating whether Cached I/O or Direct I/O is being used. In Cached I/O mode, all reads are buffered in cache memory. In Direct I/O mode, reads are not buffered in cache memory. Data is transferred to cache and the host concurrently. If the same data block is read again, it comes from cache memory. (The IO Policy applies to reads on a specific volume. It does not affect the read ahead cache.)
load-balancing		A method of spreading work between two or more computers, network links, CPUs, drives, or other resources. Load balancing maximizes resource use, throughput, or response time.
LDF		Logical disk format.
mirroring		The process of providing complete data redundancy with two drives by maintaining an exact copy of one drive’s data on the second drive. If one drive fails, the contents of the other drive can be used to maintain the integrity of the system and to rebuild the failed drive.
multipathing		The firmware provides support for detecting and using multiple paths from the HPE Smart Array P824i-p MR Gen10 Controllers to the SAS devices that are in enclosures. Devices connected to enclosures have multiple paths to them. With redundant paths to the same port of a device, if one path fails, another path can be used to communicate between the controller and the device. Using multiple paths with load balancing, instead of a single path, can increase reliability through redundancy.
offline		A drive is offline when it is part of a volume but its data is not accessible to the volume.
OS		Operating system.
patrol read		A process that checks the drives in a storage configuration for drive errors that could lead to drive failure and lost data. The patrol read operation can find and sometimes fix any potential problem with drives before host access. This enhances overall system performance because error recovery during a normal I/O operation might not be necessary.
patrol read rate		The user-defined rate at which patrol read operations are run on a computer system.
physical drive or disk (PD)		A disk used to emphasize a contract with virtual disks.
RAID		A group of multiple, independent drives that provide high performance by increasing the number of drives used for saving and accessing data. A RAID array improves input/output (I/O) performance and data availability. The group of drives appears to the host system as a single storage unit or as multiple volumes. Data throughput improves because several drives can be accessed simultaneously. RAID configurations also improve data storage availability and fault tolerance. Redundant RAID levels (RAID levels 1, 5, 6, 10, 50, and 60) provide data protection.
RAID 0		Uses data striping on two or more drives to provide high data throughput, especially for large files in an environment that requires no data redundancy.
RAID 1		Uses data mirroring on pairs of drives so that data written to one drive is simultaneously written to the other drive. RAID 1 works well for small databases or other small applications that require complete data redundancy.
RAID 5		Uses data striping and parity data across three or more drives (distributed parity) to provide high data throughput and data redundancy, especially for applications that require random access.
RAID 6		Uses data striping and parity data across three or more drives (distributed parity) to provide high data throughput and data redundancy, especially for applications that require random access. RAID 6 can survive the failure of two drives.
RAID 10		A combination of RAID 0 and RAID 1 that uses data striping across two mirrored arrays. It provides high data throughput and complete data redundancy.
RAID 50		A combination of RAID 0 and RAID 5 that uses data striping across two arrays with parity data. It provides high data throughput and complete data redundancy.
RAID 60		A combination of RAID 0 and RAID 6 that uses data striping across two arrays with parity data. It provides high data throughput and complete data redundancy. RAID 60 can survive the failure of two drives in each RAID set in the spanned array.
RAID level		A volume property indicating the RAID level of the volume. HPE Smart Array MR Controllers support RAID levels 0, 1, 5, 6, 10, 50, and 60.
RAID transformation		A feature in RAID subsystems that allows changing a RAID level to another level without powering down the system.
raw capacity		A drive property indicating the actual full capacity of the drive before any coercion mode is applied to reduce the capacity.
read policy		A controller attribute indicating the current Read Policy mode. In Always Read Ahead mode, the controller reads sequentially ahead of requested data and stores the additional data in cache memory, anticipating that the data will be needed soon. This speeds up reads for sequential data, but there is little improvement when accessing random data. In No Read Ahead mode (known as Normal mode in WebBIOS), read ahead capability is disabled.
rebuild		The regeneration of all data to a replacement drive in a redundant volume after a drive failure. A drive rebuild normally occurs without interrupting normal operations on the affected volume, though some degradation of performance of the drive subsystem can occur.
rebuild rate		The percentage of central processing unit (CPU) resources devoted to rebuilding data onto a new drive after a drive in a storage configuration has failed.
reclaim volume		A method of undoing the configuration of a new volume. If you highlight the volume in the Configuration wizard and click Reclaim, the individual drives are removed from the volume configuration.
redundancy		A property of a storage configuration that prevents data from being lost when one drive fails in the configuration.
redundant configuration		A volume that has redundant data on drives in the array that can be used to rebuild a failed drive. The redundant data can be parity data striped across multiple drives in a array, or it can be a complete mirrored copy of the data stored on a second drive. A redundant configuration protects the data in case a drive fails in the configuration.
SAS		Acronym for Serial-Attached SCSI. SAS is a serial, point-to-point, enterprise-level device interface that leverages the Small Computer System Interface (SCSI) protocol set. The SAS interface provides improved performance, simplified cabling, smaller connectors, lower pin count, and lower power requirements when compared to parallel SCSI.
SATA		Acronym for Serial Advanced Technology Attachment. A physical storage interface standard. SATA is a serial link that provides point-to-point connections between devices. The thinner serial cables allow for better airflow within the system and permit smaller chassis designs.
SCSI device type		A drive property indicating the type of the device, such as drive.
serial no.		A controller property indicating the manufacturer-assigned serial number.
spare drive		A standby drive that can automatically replace a failed drive in a volume and prevent data from being lost. A spare drive can be dedicated to a single redundant array or it can be part of the global spare drive pool for all arrays controlled by the controller. When a drive fails, the application automatically uses a spare drive to replace it and then rebuilds the data from the failed drive to the spare drive. Spare Drives can be used in RAID 1, 5, 6, 10, 50, and 60 storage configurations.
stripe size		A volume property indicating the length of the interleaved data segments that the RAID controller writes across multiple drives, not including parity drives. For example, consider a stripe that contains 64 KB of drive space and has 16 KB of data residing on each drive in the stripe. In this case, the stripe size is 64 KB, and the strip size is 16 KB. The user can select the stripe size.
striping		A technique used to write data across all drives in a volume. Each stripe consists of consecutive volume data addresses that are mapped in fixed-size units to each drive in the volume using a sequential pattern. For example, if the volume includes five drives, the stripe writes data to drives one through five without repeating any of the drives. The amount of space consumed by a stripe is the same on each drive. Striping by itself does not provide data redundancy. Striping in combination with parity does provide data redundancy.
strip size		The portion of a stripe that resides on a single drive in the array.
subvendor ID		A controller property that lists additional vendor ID information about the controller.
transformation		The process of moving volumes and spare drive drives from one controller to another by disconnecting the drives from one controller and attaching them to another one. The firmware on the new controller will detect and retain the volume information on the drives.
transformation rate		The user-defined rate at which an array modification operation is carried out.
URI		Uniform Resource Identifier.
vendor ID		A controller property indicating the vendor-assigned ID number of the controller.
vendor info		A drive property listing the name of the vendor of the drive.
volume		An entity within a SCSI target that executes I/O commands. A storage unit created by a RAID controller from one or more drives. Although a volume can be created from several drives, it is seen by the operating system as a single drive. Depending on the RAID level used, the volume can retain redundant data in case of a drive failure.
volume state		A volume property indicating the condition of the volume. Examples include Optimal and Degraded.
write-back		In Write-Back Caching mode, the controller sends a data transfer completion signal to the host when the controller cache has received all of the data in a drive write transaction. Data is written to the drive subsystem in accordance with policies set up by the controller. These policies include the amount of dirty/clean cache lines, the number of cache lines available, and elapsed time from the last cache flush.
write policy		See Default Write Policy.
write-through		In Write-Through Caching mode, the controller sends a data transfer completion signal to the host when the drive subsystem has received all of the data and has completed the write transaction to the drive.