LSI MegaRaid: Patrol Read и Consistency Check

MegaRAID Patrol read

MegaRAID Patrol read periodically verifies all sectors(including system reserved area) of drives including hot spare connected to a controller. The goal is to protect data integrity by detecting drive failure before the failure can damage data. The corrective actions depend on the drive group configuration and the type of errors.
Patrol read starts only when the controller is idle for a defined period of time and no other background tasks are active, though it can continue to run during heavy I/O processes.

Note: A patrol read is initiated only when the controller is idle for a defined time period and has no other background activities, such as Background initialization, rebuilding, consistency check etc..

Read Patrol is an adaptive process that runs as a background operation on the MegaRAID controller. It is adaptive, so that during periods of high disk access by the host applications, read patrol activity is lessened, and thus does not interfere with the applications.

During periods of lesser disk accesses by host applications, the read patrol activity can be increased. The purpose is to make sure that all stripes of a logical drive are read within a reasonable period of time, thus trying to ensure that the user’s data is available when needed. This process causes the drives to read the data by issuing read-verify commands. By using the read-verify command, the data from the drives is not transferred to the MegaRAID adapter unless an error is detected and reported by one or more drives included in the stripe. If a single drive reports an error within the stripe, the read patrol function initiates read commands to all the other stripe unit drives and the data for this single failing stripe unit is recreated by the MegaRAID adapter from the remaining data and parity stripe units.

After recreating this data, the adapter then issues a write-verify command to the drive that reported the error on the read-verify command and writes this recreated portion of the stripe to that drive. After this write completes successfully, this is now a known good stripe, and read patrol can continue with the next stripe. In the event that two or more drives report errors during the read-verify portion of the read patrol, the failing stripe will be added to the Bad Stripe Table.

Просмотр состояния адаптера


Просмотр состояния  всех логических дисков в RAID


Опции Patrol Read

Description Sets Patrol Read options on a single controller, multiple controllers, or all controllers:

Получение информации о Read Patrol


Включение автоматического сканирования Read Patrol


Выключение автоматического сканирования Read Patrol


Просмотр текущего коэффициента чтения


Минимизация/сокращение влияния сканирования Read Patrol на дисковую подсистему ввода/вывода  путем уменьшения  коэффициента чтения с дефолтных 30% до,например, 5%


Ручной старт/запуск сканирования Read Patrol


Остановка сканирования Read Patrol


Установка/изменение интервала сканирования Read petrol c  дефолтных 7 дней(168 часов) на, например, 30 дней(720 часов)

Значение временного интервала устанавливается в часах


Исправление media-ошибок во время Patrol Read


MegaRAID consistency check

MegaRAID consistency checking is different from Read Patrol in that consistency checking reads all portions of a stripe, computing parity from the data portions of the stripe and then comparing the computed parity to the parity read from the drive. Not valid to RAID0 of course.

If the compare fails, the computed parity is then written to the appropriate drive. This process can impact the performance on the controller.

The consistency check can be started manually or automatically, both can set/start by MegaRAID Storage Manager or MegaCli(MegaCli64), In this article, I’ll be using example of MegaCli command line.

Consistency checking is automatically started in background mode at the time a parity type logical drive is created, and at this time each parity portion of every stripe is created from the existing data portions of the stripe and written to the appropriated drive.

By default, MegaRAID consistency check is enabled to concurrent mode, runs every 168 hours at up to 30% performance impact, you can check and set the values according to your business environment.


Просмотр текущего статуса, режима работы, даты следующего планового запуска, интервала запуска Consistency Check


Изменение запланированного времени старта сканирования Consistency Check


Просмотр того, что делает  Consistency Check в данный момент

В момент выполнения сканирования,например, вывод может быть таким


Просмотр коэффициента сканирования Consistency Check


Уменьшение коэффициента сканирования до 5% с целью уменьшения влияния сканирования на производительность дисковой подсистемы


Изменение интервала сканирования с дефолтных 168 часов(7 дней) до,например,720 часов(30 дней)


Ручной старт/запуск сканирования Consistency Check

Если появляется ошибка типа

то выполняем


Остановка сканирования Consistency Check


Отключение сканирования  Consistency Check


Изменение режима работы с дефолтного concurrent на sequencial


Изменение режима работы на concurrent


После изменения режима с Отключено на режим concurrent/sequencial следующая запланированная Consistency Check будет проводиться в 2135 году,поэтому дополнительно необходимо установить время запланированного запуска снова




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