Dell™ PowerEdge™ Expandable RAID Controller 5/i and 5/E User's Guide
A
Adapter
An adapter enables the computer system to access peripheral devices by converting the protocol of one bus or interface to another. An adapter may also provide specialized function. For example, a RAID controller is a type of adapter that provides RAID functions. Adapters may reside on the system board or be an add-in card. Other examples of adapters include network and SCSI adapters.
Adaptive Read Ahead
Adaptive read ahead is a read policy that specifies that the controller begins using read-ahead caching if the two most recent disk accesses occurred in sequential sectors. If all read requests are random, the algorithm reverts to Non read ahead; however, all requests are still evaluated for possible sequential operation.
B
Background Initialization
Background initialization is the automatic check for media errors on physical disks. It ensures that striped data segments are the same on all physical disks in a virtual disk. The difference between a background initialization and a consistency check is that a background initialization is automatic for new virtual disks. The operation starts within five minutes after you create the disk.
Baseport
Base register of the memory address range provided by the host.
Battery Backup Unit (BBU)
The battery backup unit protects the integrity of the cached data on the controller by providing backup power if there is a complete AC power failure or a brief power outage.
BIOS
Acronym for basic input/output system. Your computer's BIOS contains programs stored on a flash memory chip. The BIOS controls the following: communications between the microprocessor and peripheral devices, such as the keyboard and the video adapter, and miscellaneous functions, such as system messages.
BIOS Configuration Utility
The BIOS Configuration Utility configures and maintains RAID disk groups and virtual disks, and manages the RAID system. Because the utility resides in the controller BIOS, its operation is independent of the operating systems on your system. The BIOS Configuration Utility, also known as Ctrl-R, is built on elements called controls. Each control performs a function. The functions include procedures you can use to configure physical disks and virtual disks.
C
Cache
Fast memory that holds recently accessed data. Using cache speeds subsequent access to the same data. It is most often applied to processor-memory access but also can be used to store a copy of data accessible over a network. 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 utilizing a high speed memory buffer, referred to as a "cache," in order to speed up the overall read or write performance. This cache can be accessed at a higher speed than a disk subsystem. To improve read performance, the cache usually contains the most recently accessed data, as well as data from adjacent disk sectors. To improve write performance, the cache may temporarily store data in accordance with its write back policies. See the definition of Write-Back for more information.
Consistency Check
An operation to verify that all stripes in a virtual disk with a redundant RAID level are consistent and automatically fix any errors. For RAID 5, 10, and 50 arrays, consistency check verifies correct parity data for each stripe. For RAID 1 arrays, this operation verifies correct mirror data for each stripe.
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 physical disk or the keyboard. In Storage Management, the hardware or logic that interacts with storage devices to write and retrieve data and perform storage management. RAID controllers perform RAID functions such as striping and mirroring to provide data protection.
D
DDR SDRAM
Acronym for Double Data Rate Synchronous Dynamic Random Access Memory. This is a type of SDRAM that provides data throughput at double the rate of conventional SDRAM. It uses a bursting technique to predict the address of the next memory location to be accessed and allows two data transfers on each clock cycle.
Disk
A non-volatile, randomly addressable, rewriteable mass storage device, including both rotating magnetic and optical storage devices and solid-state storage devices, or non-volatile electronic storage elements.
Disk Array
A set of physical disks attached to a controller or adapter.
Disk Group
A logical grouping of disks attached to a RAID controller on which one or more virtual disks can be created, such that all virtual disks in the disk group use all of the physical disks in the disk group.
Disk Migration
Moving a virtual disk or a hot spare from one controller to another by detaching the physical disks and re-attaching them to the new controller.
Disk Roaming
Moving disksfrom one slot to another on a controller.
Disk Subsystem
A collection of disks and the hardware that controls them and connects them to one or more controllers. The hardware can include an intelligent controller, or the disks can attach directly to a system I/O bus controller.
Distributed Parity
Parity involves an extra bit added to a byte or word to reveal errors in storage (in RAM or disk) or transmission. Parity is used to generate a set of redundancy data from two or more parent data sets. The redundancy data can be used to rebuild one of the parent data sets. In distributed parity, the parity data are distributed among all the physical disks in the system. If a single physical disk fails, it can be rebuilt from the parity of the applicable data on the remaining physical disks.
DKMS
Acronym for Dynamic Kernel Module Support. Designed by Dell™, DKMS creates a framework in which kernel-dependent module source can reside so that it is easy to rebuild modules as you upgrade kernels. DKMS is used in the upgrade process for drivers for Red Hat® Linux and SUSE® Linux Enterprise Server.
DUD
Acronym for driver update diskette. A DUD is an image of a diskette stored as a regular file. To use it, you have to create a real diskette from this file. The steps used to create the diskette depend on how the image is supplied.
E
ECC Errors
Acronym for error correcting code. ECC errors occur in the memory and can corrupt cached data so that it must be discarded. Single-bit ECC errors can be handled by the firmware and do not disrupt normal operation. A notification will be sent if the number of single-bit errors exceeds a threshold value. ECC double-bit errors are more serious, as they result in corrupted data and data loss.
Enclosure
A structure, such as a system, which contains physical disks that are grouped together to create virtual disks.
Enclosure Management
Intelligent monitoring of the disk subsystem by software and/or hardware. The disk subsystem can be part of the host system or can reside in an external disk enclosure. Enclosure management helps you stay informed of events in the disk subsystem, such as a physical disk or power supply failure. Enclosure management increases the fault tolerance of the disk subsystem.
Exclusive-OR
A Boolean operation used to create a parity bit that can be used to restore data affected by a damaged file or failed physical disk. The management utility compares data from two physical disks and creates a parity bit that is stored on a third physical disk. This operation is used for RAID levels that use parity bits, such as RAID 5, which used distributed parity. Also known as X-OR.
F
Failed Physical Disk
A physical disk that has ceased to function, that consistently functions improperly, or that is inaccessible.
Fault Tolerance
Fault tolerance is the capability of the disk subsystem to undergo a single drive failure per disk group without compromising data integrity and processing capability. The PERC 5 controllers provide this support through redundant virtual disks in RAID levels 1, 5, 10 and 50.
Fault tolerance is often associated with system availability because it allows the system to be available during drive failures. In case a disk fails, the PERC 5 controllers support hot spare disks 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 disk or from a network and then passes control to the operating system.
Foreign Configuration
A RAID configuration that already exists on a replacement physical disk that you install in a system. You can import the existing configuration to the RAID controller or clear it so you can create a new one.
Format
The process of writing a specific value to all data fields on a physical disk, to map out unreadable or bad sectors. Because most physical disks are formatted when manufactured, formatting is usually done only if a physical disk generates many media errors.
G
GB
Acronym for gigabyte(s). A gigabyte equals 1,024 megabytes or 1,073,741,824 bytes (2^30 bytes).
H
Host System
Any system on which the RAID controller is installed. Mainframes, workstations, and personal systems can all be considered host systems.
Hot Spare
An idle, powered on, stand-by physical disk ready for immediate use in case of disk failure. It does not contain any user data. A hot spare can be dedicated to a single redundant virtual disk or it can be part of the global hot-spare pool for all virtual disks controlled by the controller.
When a disk fails, the controllers' firmware automatically replaces and rebuilds the data from the failed physical disk to the hot spare. Data can be rebuilt only from virtual disks with redundancy (RAID levels 1, 5, 10, or 50; not RAID 0), and the hot spare must have sufficient capacity.
Hot Swap
Replacement of a failed component while the system is running and operating normally.
I
Initialization
The process of writing zeros to the data fields of a virtual disk and, in fault tolerant RAID levels, generating the corresponding parity to put the virtual disk in a Ready state. Initializing erases previous data and generates parity so that the virtual disk will pass a consistency check. Virtual disks can work without initializing, but they can fail a consistency check because the parity fields have not been generated.
Inter-IC
Inter-IC, also known as I2C, is a multi-master bus, meaning that more than one chip can be connected to the same bus. Each chip can act as a master and initiate a data transfer.
M
MB
Acronym for megabyte(s). The term megabyte means 1,048,576 bytes (2^20 bytes); however, when referring to hard drive storage, the term is often rounded to mean 1,000,000 bytes.
Mirroring
The process of providing complete redundancy using two physical disks, by maintaining an exact copy of one physical disk's data on the second physical disk. If one physical disk fails, the contents of the other physical disk can be used to maintain the integrity of the system and to rebuild the failed physical disk.
Multi-bit ECC Errors
ECC errors are errors that occur in the memory, which can corrupt cached data so that it has to be discarded. ECC double-bit errors are serious, as they result in corrupted data and data loss. In case of double-bit ECC errors, contact Dell Technical Support.
N
Non Read Ahead
Non read ahead is a cache read policy. If you select Non read ahead in the BIOS Configuration Utility, the controller does not read sequentially ahead of requested data and store the additional data in cache memory, anticipating that the data will be needed soon. Non read ahead is most effective when accessing random data.
Non Redundant Virtual Disk
A non-redundant virtual disk is one which does not have redundant data on physical disks that can be used to rebuild a failed physical disk. A RAID 0 virtual disk consists of data striped across the physical disks, without disk mirroring or parity to provide redundancy. This provides for high data throughput but offers no protection in case of a physical disk failure.
Ns
Acronym for nanosecond(s), one billionth of a second.
NVRAM
Acronym for non-volatile random access memory. A storage system that does not lose the data stored on it when power is removed. NVRAM is used to store configuration data on the RAID controller.
O
Offline
A physical disk is offline when it is part of a virtual disk but its data is not accessible to the virtual disk.
Online
An online device is a device that is accessible.
Online Capacity Expansion
Operation to add capacity to an existing virtual disk by adding an additional physical disk while the host system is active, and without affecting data availability.
Operating Environment
An operating environment can include the host system where physical disks are attached, any I/O buses and controllers, the host operating system and any additional software required to manage the virtual disk. For host-based arrays, the operating environment includes I/O driver software for the member disks but does not include array management software, which is regarded as part of the array itself.
P
Parity
An extra bit added to a byte or word to reveal errors in storage (in RAM or disk) or transmission. Parity is used to generate a set of redundancy data from two or more parent data sets. The redundancy data can be used to rebuild one of the parent data sets. However, parity data does not fully duplicate the parent data sets. In RAID, this method is applied to entire physical disks or stripe elements across all physical disks in a virtual disk. Parity consists of dedicated parity, in which the parity of the data on two or more physical disks is stored on an additional physical disk, and distributed parity, in which the parity data are distributed among all the physical disks in the system. If a single physical disk fails, it can be rebuilt from the parity of the applicable data on the remaining physical disks.
Partition
A logical structure on a contiguous segment of storage on a physical disk or virtual disk recognized by an operating system.
Patrol Read
A preventive measure that includes review of your system for possible physical disk errors that could lead to drive failure and damage data integrity. The Patrol Read operation can find and possibly resolve any potential problem with physical disks prior to host access. This can enhance overall system performance because error recovery during a normal I/O operation may not be necessary.
PHY
The interface required to transmit and receive data packets transferred across the serial bus.
Each PHY can form one side of the physical link in a connection with a PHY on a different Dell-qualified SATA device. The physical link contains four wires that form two differential signal pairs. One differential pair transmits signals, while the other differential pair receives signals. Both differential pairs operate simultaneously and allow concurrent data transmission in both the receive and the transmit directions.
Physical Disk
A non-volatile, randomly addressable device for storing data. Physical disks are rewritable and commonly referred to as disk drives.
Physical Disk States
A physical disk can be in one of the following states:
Un-configured Good: A disk accessible to the RAID controller but not configured as a part of a virtual disk or as a hot spare.
Hot Spare: A physical disk that is configured as a hot spare.
Online: A physical disk can be accessed by the RAID controller and will be part of the virtual disk.
Rebuild: A physical disk to which data is being written to restore full redundancy for a virtual disk.
Failed: A physical disk that was originally configured as Online or Hot Spare, but on which the firmware detects an unrecoverable error.
Un-configured Bad: A physical disk on which the firmware detects an unrecoverable error; the physical disk was Un-configured Good or the physical disk could not be initialized.
Missing: A physical disk that was Online, but which has been removed from its location.
Offline: A physical disk that is part of a virtual disk but which has invalid data as far as the RAID configuration is concerned.
None: A physical disk with the unsupported flag set. An Un-configured Good or Offline physical disk that has completed the prepare for removal operation.
Protocol
A set of formal rules describing how to transmit data, generally across a network or when communicating with storage subsystems. Low-level protocols define the electrical and physical standards to be observed, bit- and byte-ordering, and the transmission and error detection and correction of the bit stream. High-level protocols deal with the data formatting, including the message syntax, the terminal to system dialogue, character sets, sequencing of messages, etc.
R
RAID
Acronym for Redundant Array of Independent Disks (originally Redundant Array of Inexpensive Disks). It is an array of multiple independent physical disks managed together to yield higher reliability and/or performance exceeding that of a single physical disk. The virtual disk appears to the operating system as a single storage unit. I/O is expedited because several disks can be accessed simultaneously. Redundant RAID levels (RAID levels 1, 5, 10, and 50), provide data protection.
RAID Level Migration
RAID level migration (RLM) changes the array from one RAID level to another. It is used to move between optimal RAID levels. You can perform a RLM while the system continues to run, without having to reboot. This avoids downtime and keeps data available to users.
RAID Levels
A set of techniques applied to disk groups to deliver higher data availability, and/or performance characteristics to host environments. Each virtual disk must have a RAID level assigned to it.
RAID Management Utility
A RAID management utility is used to configure physical disks into disk groups and virtual disks. The BIOS Configuration Utility is also known as Ctrl-R. Use the BIOS Configuration Utility if no operating system has been installed yet on the controller. The BIOS Configuration Utility is built on elements called controls. Each control performs a function. The functions include procedures you can use to configure physical disks and virtual disks.
The Dell OpenManage™ Storage Management configures the disks after you have installed the operating system. Storage Management enables you to perform controller and enclosure functions for all supported RAID and non-RAID controllers and enclosures from a single graphical or command-line interface without requiring the use of the controller BIOS utilities.
SAS RAID Storage Manager configures, monitors, and maintains the PERC 5 controllers, battery backup units, and other devices running on a server.
Read-Ahead
A memory caching capability in some controllers that allows them to read sequentially ahead of requested data and store the additional data in cache memory, anticipating that the additional data will be needed soon. Read-ahead supplies sequential data faster, but is not as effective when accessing random data.
Rebuild
The regeneration of all data to a replacement disk in a redundant virtual disk (RAID level 1, 5, 10, or 50) after a physical disk failure. A disk rebuild normally occurs without interrupting normal operations on the affected virtual disk, though some degradation of performance of the disk subsystem can occur.
Rebuild Rate
The percentage of central processing unit (CPU) resources devoted to rebuilding.
Reconstruct
The act of remaking a virtual disk after changing RAID levels or adding a physical disk to an existing virtual disk.
Redundancy
The provision of multiple interchangeable components to perform a single function to cope with failures and errors. Common forms of hardware redundancy are disk mirroring, implementations of parity disks, or distributed parity.
Redundant Virtual Disk
A redundant virtual disk is one which has redundant data on physical disks in the disk group that can be used to rebuild a failed physical disk. A virtual disk can use disk striping across the physical disks, disk mirroring or parity to provide redundancy. This offers protection in case of a physical disk failure.
Replacement Disk
A physical disk replacing a failed member disk in a virtual disk.
Replacement Unit
A component or collection of components in a system or subsystem that is always replaced as a unit when any part of the collection fails. Typical replacement units in a disk subsystem include disks, controller logic boards, power supplies and cables.
RPM
Acronym for Red Hat Package Manager. RPM is a software manager used to install, remove, query, and verify the software on your system. RPMs are used in the driver update procedures for Red Hat Enterprise Linux and SUSE LINUX Enterprise Server (SLES).
S
SAS
Acronym for Serial Attached SCSI. SAS is a serial, point-to-point, enterprise-level device interface that leverages the proven 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. PERC 5 controllers leverage a common electrical and physical connection interface that is compatible with Serial ATA technology.
SATA
Acronym for Serial Advanced Technology Attachment. A physical storage interface standard, 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.
SCSIport
The SCSIport driver is a feature of the Microsoft® Windows® storage architecture, delivering SCSI commands to the storage targets. The SCSIport driver works well with storage using parallel SCSI.
Single Bit ECC Errors
ECC stands for error correcting code. ECC errors are errors that occur in the memory, which can corrupt cached data so that it has to be discarded. Single-bit ECC errors can be handled by the firmware and do not disrupt normal operation. A notification will be sent if the number of single-bit errors exceeds a threshold value.
SMART
Acronym for Self-Monitoring Analysis and Reporting Technology. The self-monitoring analysis and reporting technology (SMART) feature monitors the internal performance of all motors, heads, and drive electronics to detect predictable drive failures. This feature helps monitor drive performance and reliability, and protects the data on the drive. When problems are detected on a drive, you can replace or repair the drive without losing any data.
SMART-compliant disks have attributes for which data (values) can be monitored to identify changes in values and determine whether the values are within threshold limits. Many mechanical failures and some electrical failures display some degradation in performance before failure
SMP
Acronym for Serial Management Protocol. SMP communicates topology management information directly with an attached SAS expander device. Each PHY on the controller can function as an SMP initiator.
Span
A RAID technique used to combine storage space from groups of physicals disks into a RAID 10 or 50 virtual disk.
Spare
A physical disk available to replace another physical disk in case that physical disk fails.
SSP
Acronym for Serial SCSI Protocol. SSP enables communication with other SAS devices. Each PHY on the SAS controller can function as an SSP initiator or SSP target.
Storport
The Storport driver has been designed to replace SCSIport and work with Windows 2003 and beyond. In addition, it offers better performance for RAID controllers, providing higher I/O throughput rates, improved manageability, and an upgraded miniport interface. For example, while SCSIport allows a maximum of 254 commands per controller, Storport allows 254 command per logical unit number (LUN).
STP
Acronym for Serial Tunneling Protocol, STP, enables communication with a Dell-qualified SATA device through an attached expander. Each PHY on the SAS controller can function as an STP initiator.
Stripe Element
A stripe element is the portion of a stripe that resides on a single physical disk. See also striping.
Stripe Element Size
The total disk space consumed by a stripe not including a parity disk. For example, consider a stripe that contains 64 KB of disk space and has 16 KB of data residing on each disk in the stripe. In this case, the stripe element size is 16 KB and the stripe size is 64 KB.
Striping
Disk striping writes data across all physical disks in a virtual disk. Each stripe consists of consecutive virtual disk data addresses that are mapped in fixed-size units to each physical disk in the virtual disk using a sequential pattern. For example, if the virtual disk includes five physical disks, the stripe writes data to physical disks one through five without repeating any of the physical disks. The amount of space consumed by a stripe is the same on each physical disk. The portion of a stripe that resides on a physical disk is a stripe element. Striping by itself does not provide data redundancy. Striping in combination with parity does provide data redundancy.
T
TBBU
Acronym for Transportable Battery Backup Unit. The TBBU protects the integrity of the cached data on the controller by providing backup power if there is a complete AC power failure or a brief power outage. A transportable battery backup unit can be used to move a controller's cached data that has not been written to the disk to a replacement controller. After you install the transportable battery backup unit on the new controller, it flushes the unwritten data preserved in the cache to the disk through the new controller.
V
Virtual Disk
A virtual disk refers to storage created by a RAID controller from one or more physical disks. Although a virtual disk may be created from several physical disks, it is seen by the operating system as a single disk. Depending on the RAID level used, the virtual disk may retain redundant data in case of a disk failure.
W
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 the data in a disk write transaction. Data is written to the disk 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, elapsed time from the last cache flush, and others.
Write-Through
In write-through caching mode, the controller sends a data transfer completion signal to the host when the disk subsystem has received all the data and has completed the write transaction to the disk.
X
XP
XP is a Microsoft Windows operating system. Released in 2001, it is built on the Windows 2000 kernel, making it more stable and reliable than previous versions of Windows. It includes an improved user interface and more mobility features, such as plug and play features used to connect to wireless networks.
