MegaRAID Glossar

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In diesem Artikel finden Sie ein Verzeichnis aller Begriffe eines Avago RAID Controllers. Die Auflistung stammt aus dem MegaRaid SAS Software User Guide.[1]

Begriffserklärungen

access policy:
A virtual drive property indicating what kind of access is allowed for a particular virtual drive. The possible values are Read/Write, Read Only, or Blocked.

alarm enabled:
A controller property that indicates whether the controller’s onboard alarm is enabled.

alarm present:
A controller property that indicates whether the controller has an onboard alarm. If present and enabled, the alarm is sounded for certain error conditions.

array:
See drive group.

BBU present:
A controller property that indicates whether the controller has an onboard battery backup unit to provide power in case of a power failure.

BGI rate:
A controller property indicating the rate at which the background initialization of virtual drives will be carried out.

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.

cache flush interval:
A controller property that indicates how often the data cache is flushed.
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 virtual drive.

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 4,196 MB, and a 4-GB from another manufacturer might be 4,128 MB. These drives could be coerced to a usable capacity of 4,088 MB each for use in a drive group 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 virtual drive with a redundant RAID level are consistent and that automatically fixes any errors. For RAID 1 drive groups, 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. RAID controllers perform RAID functions such as striping and mirroring to provide data protection. MegaRAID Storage Manager software runs on LSI SAS controllers.

copyback:
The procedure used to copy data from a source drive of a virtual drive to a destination drive that is not a part of the virtual drive. The copyback operation is often used to create or restore a specific physical configuration for a drive group (for example, a specific arrangement of drive group 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 hot spare. The failed drive is replaced with a new drive. Then the data is copied from the hot spare to the new drive, and the hot spare reverts from a rebuild drive to its original hot spare status. The copyback operation runs as a background activity, and the virtual drive is still available online to the host.

current write policy:
A virtual drive property that indicates whether the virtual drive 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.

default write policy:
A virtual drive property indicating whether the default write policy is Write Through or Write Back. 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.

device port count:
A controller property indicating the number of ports on the controller.

drive cache policy:
A virtual drive property indicating whether the virtual drive cache is enabled, disabled, or unchanged from its previous setting.

drive group:
A group of drives attached to a RAID controller on which one or more virtual drives can be created. All virtual drives in the drive group use all of the drives in the drive group.

drive state:
A drive property indicating the status of the drive. A drive can be in one of the following states:
- Unconfigured Good: A drive accessible to the RAID controller but not configured as a part of a virtual drive or as a hot spare.
- Hot Spare: A drive that is configured as a hot spare.
- Online: A drive that can be accessed by the RAID controller and will be part of the virtual drive.
- Rebuild: A drive to which data is being written to restore full redundancy for a virtual drive.
- Failed: A drive that was originally configured as Online or Hot Spare, but on which the firmware detects an unrecoverable error.
- Unconfigured Bad: A drive on which the firmware detects an unrecoverable error; the drive was Unconfigured Good or the drive could not be initialized.
- Missing: A drive that was Online, but which has been removed from its location.
- Offline: A drive that is part of a virtual drive but which has invalid data as far as the RAID configuration is concerned.
- None: A drive with an unsupported flag set. An Unconfigured Good or Offline drive that has completed the prepare for removal operation.

drive subsystem:
A collection of drives and the hardware that controls them and connects them to one or more controllers. The hardware can include an intelligent controller, or the drives can attach directly to a system I/O bus controller.

drive type:
A drive property indicating the characteristics of the drive.

fast initialization:
A mode of initialization that quickly writes zeroes to the first and last sectors of the virtual drive. This allows you to immediately start writing data to the virtual drive while the initialization is running in the background.

fault tolerance:
The capability of the drive subsystem to undergo a single drive failure per drive group without compromising data integrity and processing capability. LSI SAS RAID controllers provides fault tolerance through redundant drive groups in RAID levels 1, 5, 6, 10, 50, and 60. They also support hot spare 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 drive or from a network and then passes control to the operating system.

foreign configuration:
A RAID configuration that already exists on a replacement set of drives that you install in a computer system. MegaRAID Storage Manager software allows you to import the existing configuration to the RAID controller, or you can clear the configuration so you can create a new one.

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.

hole:
In MegaRAID Storage Manager, a hole is a block of empty space in a drive group that can be used to define a virtual drive.

host interface:
A controller property indicating the type of interface used by the computer host system: for example, PCIX.

host port count:
A controller property indicating the number of host data ports currently in use.

host system:
Any computer system on which the controller is installed. Mainframes, workstations, and standalone desktop systems can all be considered host systems.

hot spare:
A standby drive that can automatically replace a failed drive in a virtual drive and prevent data from being lost. A hot spare can be dedicated to a single redundant drive group or it can be part of the global hot spare pool for all drive groups controlled by the controller.
When a drive fails, MegaRAID Storage Manager software automatically uses a hot spare to replace it and then rebuilds the data from the failed drive to the hot spare. Hot spares can be used in RAID 1, 5, 6, 10, 50, and 60 storage configurations.

initialization:
The process of writing zeros to the data fields of a virtual drive and, in fault-tolerant RAID levels, generating the corresponding parity to put the virtual drive in a Ready state. Initialization erases all previous data on the drives. Drive groups will work without initializing, but they can fail a consistency check because the parity fields have not been generated.

IO policy:
A virtual drive 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 virtual drive. It does not affect the read ahead cache.)

learning cycle:
A battery calibration operation performed by a RAID controller periodically to determine the condition of the battery.

load-balancing:
A method of spreading work between two or more computers, network links, CPUs, drives, or other resources. Load balancing is used to maximize resource use, throughput, or response time.

media error count:
A drive property indicating the number of errors that have been detected on the drive media.

migration:
The process of moving virtual drives and hot spare 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 virtual drive information on the drives.

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 RAID 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.

name:
A virtual drive property indicating the user-assigned name of the virtual drive.

non-redundant configuration:
A RAID 0 virtual drive with data striped across two or more drives but without drive mirroring or parity. This provides for high data throughput but offers no protection in case of a drive failure.

NVRAM:
A cronym 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 firmware and configuration data on the RAID controller.

NVRAM present:
A controller property indicating whether an NVRAM is present on the controller.

NVRAM size:
A controller property indicating the capacity of the controller’s NVRAM. offline A drive is offline when it is part of a virtual drive but its data is not accessible to the virtual drive.

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 prior to 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.

product info:
A drive property indicating the vendor-assigned model number of the drive.

product name:
A controller property indicating the manufacturing name of the controller.

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 drive group 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 virtual drives. 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 00:
Uses data striping on two or more drives in a spanned drive group 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 drive groups. 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 drive groups 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 drive groups 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 drive group.

RAID level:
A virtual drive property indicating the RAID level of the virtual drive. LSI SAS RAID controllers support RAID levels 0, 1, 5, 6, 10, 50, and 60.

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 virtual drive after a drive failure. A drive rebuild normally occurs without interrupting normal operations on the affected virtual drive, 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 virtual drive:
A method of undoing the configuration of a new virtual drive. If you highlight the virtual drive in the Configuration Wizard and click Reclaim, the individual drives are removed from the virtual drive configuration.

reconstruction rate:
The user-defined rate at which a drive group modification operation is carried out.

redundancy:
A property of a storage configuration that prevents data from being lost when one drive fails in the configuration.

redundant configuration:
A virtual drive that has redundant data on drives in the drive group that can be used to rebuild a failed drive. The redundant data can be parity data striped across multiple drives in a drive group, 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.

revertible hot spare:
When you use the Replace Member procedure, after data is copied from a hot spare to a new drive, the hot spare reverts from a rebuild drive to its original hot spare status.

revision level:
A drive property that indicates the revision level of the drive’s firmware.

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.

strip size:
The portion of a stripe that resides on a single drive in the drive group.

stripe size:
A virtual drive 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 virtual drive. Each stripe consists of consecutive virtual drive data addresses that are mapped in fixed-size units to each drive in the virtual drive using a sequential pattern. For example, if the virtual drive 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.

subvendor ID:
A controller property that lists additional vendor ID information about the controller.

uncorrectable error count
A controller property that lists the number of uncorrectable errors detected on drives connected to the controller. If the error count reaches a certain level, a drive will be marked as failed.

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.

virtual drive: A storage unit created by a RAID controller from one or more drives. Although a virtual drive can be created from several drives, it is seen by the operating system as a single drive. Depending on the RAID level used, the virtual drive can retain redundant data in case of a drive failure.

virtual drive state:
A virtual drive property indicating the condition of the virtual drive. 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.

Einzelnachweise

  1. LSI User Guide Software

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