Dell™ SAS RAID Storage Manager User’s Guide w w w. d e l l . c o m | s u p p o r t . d e l l .
Notes, Notices, and Cautions NOTE: A NOTE indicates important information that helps you make better use of your computer. NOTICE: A NOTICE indicates either potential damage to hardware or loss of data and tells you how to avoid the problem. CAUTION: A CAUTION indicates a potential for property damage, personal injury, or death. ____________________ Information in this document is subject to change without notice. © 2006–2008 Dell Inc. All rights reserved.
Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . Creating Storage Configurations Monitoring Storage Devices 2 . . . . . . . . . . . . . . . . . . . 7 . . . . . . . . . . . . . . . . . . . . . 7 Maintaining Storage Configurations . . . . . . . . . . . . . . . . . 7 Comparison of Supported Features . . . . . . . . . . . . . . . . . . 8 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Installing Dell SAS RAID Storage Manager on Linux .
Creating a RAID 1 Configuration on a SAS 5/iR Controller or on a SAS 6/iR Controller . . . . . . . . . . . . . . . . . . . . . 18 . . . 19 . . . 19 . . . 21 . . . 22 . . . 23 . . . 25 . . . . . . . . . . . . . . . . . . . . . . . . 26 Creating a New Configuration on a Dell PERC 5/i Controller or on a Dell PERC 6/i Controller . . . . . . . . . . . . . . . . . . Understanding Virtual Disk Parameters . . . . . . . . . .
Monitoring Disk Drives . . . . . . . . . . . . . . . . . . . . . . . . 34 Running a Patrol Read . . . . . . . . . . . . . . . . . . . . . . . . 34 Monitoring Virtual Disks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 . . . . . . . . . . . . . . . . . 37 . . . . . . . . . . . . . . . . . . . . . . . 37 Monitoring Rebuilds and Other Processes . 6 Maintaining and Managing Storage Configurations . . . Initializing Virtual Disks Running a Consistency Check . . . . .
A Events and Messages 51 List of System Event Messages Glossary 6 Contents . . . . . . . . . . . . . . . . . . . . 51 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction Dell® SAS RAID Storage Manager works in conjunction with the appropriate libraries and drivers to enable you to configure, monitor, and maintain storage configurations on Dell PERC 5/i, SAS 5/iR, PERC 6/i, and SAS 6/iR controllers. The Dell SAS RAID Storage Manager graphical user interface (GUI) makes it easy for you to create and manage storage configurations. NOTE: iR stands for internal RAID.
Maintaining Storage Configurations On Dell systems with the PERC 5/i, PERC 6/i, SAS 5/iR, or SAS 6/iR controller, you can use Dell SAS RAID Storage Manager to perform system maintenance tasks such as running patrol read operations, updating firmware, and running consistency checks on disk groups that support redundancy.
Table 1-1.
Introduction
Installation Dell SAS RAID Storage Manager is pre-installed on your Dell system. If you need to reinstall Dell SAS RAID Storage Manager for some reason, this section explains how to do this on the supported operating systems: Microsoft® Windows®, Red Hat® Linux, and SUSE Linux.
5 Click Next to continue. 6 On the next screen, accept the default Destination Folder, or click Change to select a different destination folder. Click Next to continue. 7 On the next screen, click Install to begin the installation. The InstallShield Wizard then installs the Dell SAS RAID Storage Manager. This can take several minutes. 8 Click Finish to complete the installation process.
• More than one copy of MegaRAID Storage Manager has been installed. This message indicates that you have installed more than one copy of Dell SAS RAID Storage Manager. (This can be done by using the rpm-force command to install the rpm file directly, which is not recommended, instead of using the install.sh file.) In such cases, you must uninstall all the rpms manually before installing Dell SAS RAID Storage Manager with the procedure listed above. • The version is already installed.
Installation
Dell SAS RAID Storage Manager Windows and Menus This chapter explains how to start Dell SAS RAID Storage Manager and describes the Dell SAS RAID Storage Manager window and menus.
3 Enter your user name and password and click Login. NOTE: If the computer is networked, this is not the network login but the login to the computer itself. This is the local administrator/root password, not a network logon password. You must enter the root/administrator username and password in order to use Full Access mode. If your user name and password are correct for the login mode you have chosen, the main Dell SAS RAID Storage Manager window appears.
• Virtual disk • Physical drive: SAS • Hot spare • Enclosure and SATA A red circle to the right of an icon indicates that the device has failed. For example, this icon indicates that a disk drive has failed or gone offline: A yellow circle to the right of an icon indicates that a device is running in a degraded state.
Event Log Panel The lower part of the Dell SAS RAID Storage Manager window displays the system event log entries. New event log entries appear during the session. Each entry has an Error Level indicating the severity of the event, a timestamp and date, and a brief description of the event. For more information about the Event Log, see Monitoring System Events.
Group Operations Menu The Group Operations menu options include Check Consistency, Show Progress, and Initialize (on Dell PERC 5/i controllers and Dell PERC 6/i controllers only). Log Menu The Log menu includes options for saving and clearing the message log. For more information, see Monitoring System Events. Help Menu On the Help menu you can select Help-> Help to view the Dell SAS RAID Storage Manager online Help file.
Dell SAS RAID Storage Manager Windows and Menus
Configuration You use Dell SAS RAID Storage Manager to create storage configurations on Dell systems with PERC 5/i, SAS 5/iR, PERC 6/i , and SAS 6/iR controllers.
Creating a RAID 0 Configuration on a SAS 5/iR Controller or on a SAS 6/iR Controller Follow these steps to create a RAID 0 configuration on a Dell system with a SAS 5/iR controller or with a SAS 6/iR controller: 1 Select a Dell SAS 5/iR or a Dell SAS 6/iR controller in the left panel of the Dell SAS RAID Storage Manager window, and then select Operations-> Configuration-> Configuration Wizard. 2 In the Configuration Wizard, select two or more available drives in the left panel.
Creating a RAID 1 Configuration on a SAS 5/iR Controller or on a SAS 6/iR Controller Follow these steps to create a RAID 1 configuration on a Dell system with a SAS 5/iR controller or a SAS 6/iR controller: 1 Select a Dell SAS 5/iR or a Dell SAS 6/iR controller in the left panel of the Dell SAS RAID Storage Manager window, and then select Operations-> Configuration-> Configuration Wizard. 2 In the Configuration Wizard, select two available drives in the left panel.
Creating a New Configuration on a Dell PERC 5/i Controller or on a Dell PERC 6/i Controller You can use the Dell SAS RAID Storage Manager Configuration Wizard to create new storage configurations on Dell systems with the PERC 5/i controller or with the PERC 6/i controller.
Understanding Virtual Disk Parameters This section describes the Virtual Disk Parameters that you can set when you use the Guided Configuration or Manual Configuration modes of the Configuration Wizard. You do not necessarily need to change these parameters when you create a storage configuration; you can leave them at their default settings. • Stripe Size: A stripe is a segment of data spread across multiple physical disks. Data segments with stripe sizes of 8, 16, 32, 64, and 128 Kbytes are supported.
Direct IO: In this 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. • Access Policy: Select the type of data access that is allowed for this logical drive: Read/Write, Read Only, or Blocked. • Disk Cache Policy: Select a disk cache setting for this disk: Unchanged, Enabled, or Disabled.
2 Select Auto Configuration and click Next. The Auto Configuration window appears. 3 On the next screen, select a redundancy option from the drop-down menu at the bottom of the Auto Configuration window: • No Redundancy: The new configuration will have no data redundancy (RAID 0). If a physical disk in the configuration fails, all data will be lost. • With Redundancy: The new configuration will have data redundancy, either by parity data (RAID 5 or RAID 6) or mirrored data (RAID 1).
d If desired, reclaim the second virtual disk. e Click the checkbox next to one or two new arrays. The Virtual Disk Properties for the selected array(s) display in the right panel. f Select one array to create a non-spanned virtual disk (RAID 0, 1, 5, or 6), or select both arrays to create a spanned virtual disk (RAID 50 and 60). NOTE: The PERC 5/i controller does not support RAID 6 or RAID 60. g Click Accept in the right panel. The new virtual disk displays. h Click Next. 6 Click Finish.
4 Choose whether you want to use existing disk groups (arrays) in the new virtual disk. The options are: • Use Existing Arrays Only • Don’t Use Existing Arrays • Use Existing and New Arrays The first and third options are disabled if there are no available existing disk groups (arrays). 5 Select the maximum number of virtual disks you want to create. The maximum number of virtual disks supported is 64.
e Click the checkbox next to one or two new arrays. The Virtual Disk Properties for the selected array(s) display in the right panel. f Select one array to create a non-spanned virtual disk (RAID 0, 1, 5, or 6), or select both arrays to create a spanned virtual disk (RAID 50 and 60). NOTE: PERC 5/i does not support RAID 6 or RAID 60. g Click Accept in the right panel. The new virtual disk displays. h Click Next. i Click Finish.
NOTICE: Be sure you do not select the disk drive on which the operating system is installed. NOTE: To remove a drive from a proposed new disk group, select the drive icon in the right panel and click the left-arrow Remove button. 5 Click Accept to accept these drives for the new RAID disk group. 6 To add a hotspare to an array, select an available drive in the left panel, and then select the array from the drop-down menu, and click Add HotSpare To. NOTE: Hot spares are not available for RAID 0.
14 Check the configuration that you have just defined. If it is acceptable, click Finish and start the initialization process (unless you selected No Initialization earlier). If you want to change a setting for all of the virtual disks, click Back to return to the previous windows. If you want to change a setting for specific virtual disks, perform the following steps: a Select a virtual disk in the New Virtual Disks panel. The Reclaim button becomes available. b Click Reclaim.
3 In the first Manual Configuration window, select two available drives in the left panel. Click the right-arrow Add button to move the selected drives to the right panel to be part of a new array. 4 Click Accept to accept these drives for a new RAID 1 disk group. 5 Select two more drives for a second RAID 1 disk group, click Add, and click Accept. 6 Click Next. The Configuration Wizard window for virtual disks appears.
c Click Yes to accept. The array displays in the top left panel under the heading Arrays. d If desired, reclaim the second virtual disk. e Click the checkbox next to one or two new arrays. The Virtual Disk Properties for the selected array(s) display in the right panel. f Change the properties for the virtual disk(s), as desired. g Click Accept to accept the configuration of the new virtual disk. h Click Next to go to the next configuration step. The Virtual Disk Summary window appears.
3 In the right panel of the Operations tab, select the disk group (array) to which the hotspare will be dedicated. 4 Click Go to create the dedicated hotspare. Using the Replace Member Feature and Revertible Hot Spares The Replace Member functionality allows a previously commissioned hot spare to be reverted back to a usable hot spare. When a drive failure occurs within a virtual disk, an assigned hot spare (dedicated or global) is commissioned and begins rebuilding until the virtual disk is optimal.
If an automatic Replace Member occurs using a source drive that was originally a hot spare (that was used in a rebuild), and a new drive added for the Replace Member operation as the target drive, the hot spare reverts to the hot spare state after a successful Replace Member operation. Manual Replace Member Operation In addition to the automatic Replace Member operation, you can perform a manual Replace Member operation.
NOTE: Dell recommends that you leave the adjustable task rates at their default settings, in order to achieve the best system performance. If you raise the task rates above the defaults, foreground tasks will run more slowly and it might seem that the system is not responding. If you lower the task rates below the defaults, rebuilds and other background tasks might run very slowly and might not complete within a reasonable time.
You can change the Read Policy, Write Policy, and other properties of a virtual disk at any time after the virtual disk is created. To do this, follow these steps: 1 Select the Logical View tab in the left panel of the Dell SAS RAID Storage Manager screen. 2 Select a virtual disk icon in the left panel of the window. 3 In the right panel, select the Operations tab, and then select Set Virtual Disk Properties. A list of Virtual Disk Properties appears in the right panel.
To start the Reconstruction Wizard, select a virtual disk icon in the left panel of the Dell SAS RAID Storage Manager window and then select Operations-> Advanced Operations-> Reconstruction Wizard from the menu.
Changing the RAID Level of a Configuration on a PERC 5/i Controller or on a PERC 6/i Controller NOTICE: Be sure to back up the data on the virtual disk before you change its RAID level. Follow these steps to change the RAID level of a RAID 1, RAID 5, or RAID 6 (PERC 6/i only) configuration with the Configuration Wizard: 1 Select the Logical View tab in the left panel of the Dell SAS RAID Storage Manager screen.
3 In the right panel, select the Operations tab and select Delete Virtual Disk. 4 Click Go. 5 When the warning message appears, click the check box to confirm that you are certain that you want to delete the virtual disk, and then click Yes to confirm that you want to delete the virtual disk. NOTE: You will be asked twice if you want to delete a virtual disk to avoid deleting the virtual disk by mistake.
2 On the menu bar, select Operations-> Configuration-> Clear Configuration. A warning message appears. NOTICE: If a configuration contains an operating system drive, the configuration cannot be cleared. 3 Click Yes to clear the configuration or No to cancel the operation. Adding a Saved Storage Configuration When you replace a controller, or when you want to duplicate an existing storage configuration on a new controller, you can add a saved configuration to the controller.
Monitoring System Events and Storage Devices The Dell SAS RAID Storage Manager enables you to monitor the status of disk drives, virtual disks, and other storage devices. This chapter explains how to use Dell SAS RAID Storage Manager to perform the following monitoring tasks. Monitoring System Events Dell SAS RAID Storage Manager monitors the activity and performance of all controllers in the system and the storage devices connected to them.
Monitoring Controllers When Dell SAS RAID Storage Manager is running, you can see the status of all controllers in the left panel of the Dell SAS RAID Storage Manager window. If the controller is operating normally, the controller icon looks like this: . If the controller has failed, a small red circle appears to the right of the icon. (See Physical/Logical View Panel for a complete list of device icons.
Running a Patrol Read The Dell PERC 5/i controller and the Dell PERC 6/i controller supports the patrol read feature. Patrol read provides a dynamic check on the virtual disk to confirm the disk is functioning properly. Patrol read runs in the background, adjusting its performance based on the patrol read settings and the i/o load on the controller. A patrol read can be used for all RAID levels and for all hotspare drives.
Patrol Read Frequency: ___________________ Continuous Patrolling: Enabled/Disabled Patrol Read Task Rate: ___________________ 7 (Optional) Select Continuous Patrolling if you want patrol read to run continuously in the background instead of running at periodic intervals. If you select Continuous Patrolling, the time interval field is grayed out. 8 Click Go to enable the patrol read properties. NOTE: Patrol read does not report on its progress while it is running.
NOTE: On Dell PERC 5/i controllers and Dell PERC 6/i controllers, you can change virtual disk properties such as Read Policy, Write Policy, IO Policy, and Access Policy after the virtual disk has been created. For more information, see Changing Virtual Disk Properties. To display a graphical view of a virtual disk, click on a virtual disk icon in the left panel of the Dell SAS RAID Storage Manager and click the Graphical View tab.
Monitoring System Events and Storage Devices
Maintaining and Managing Storage Configurations This chapter explains how to use Dell SAS RAID Storage Manager to maintain and manage storage configurations. Initializing Virtual Disks To initialize a virtual disk after you complete the configuration process on a Dell PERC 5/i controller and on a Dell PERC 6/i controller, follow these steps: 1 Select the Logical tab in the left panel of the Dell SAS RAID Storage Manager window and click the icon of the virtual disk that you want to initialize.
Running a Consistency Check You should periodically run a consistency check on fault-tolerant virtual disks that are on Dell PERC 5/i controllers and Dell PERC 6/i controllers. It is especially important to do this if you suspect that the virtual disk consistency data might be corrupted. Be sure to back up the data before running a consistency check if you think the consistency data might be corrupted.
2 In the right panel of the Dell SAS RAID Storage Manager window, select the Operations tab and select Schedule Check Consistency. The schedule options appear in the right panel.
you to import the existing configuration to the RAID controller or clear the configuration so you can create a new configuration using these drives. You can preview the foreign configuration before you decide whether to import it. NOTE: On the SAS 5/iR controller and the SAS 6/iR controller, when a disk set is moved from one controller to another, the disks are reported to SAS RAID Storage Manager as un-configured and good.
On a Dell PERC 5/i system, if a RAID 1 or RAID 5 virtual disk fails, and if hotspare disks are available, the failed drive is rebuilt automatically without any user intervention. On a Dell PERC 6/i system, if a RAID 1, RAID 5, or RAID 6 virtual disk fails, and if hotspare disks are available, the failed drive is rebuilt automatically without any user intervention. On a RAID 6 virtual disk, if there are two failed drives, the failed drives are automatically rebuilt.
4 Replace the failed disk drive with a new drive of equal or greater capacity. 5 Close the computer case, reconnect the power cord, and restart the computer. 6 Restart Dell SAS RAID Storage Manager. When the new drive spins up, the drive icon changes back to normal status, and the rebuild process begins automatically.
Making a Drive Offline or Missing If a disk drive is currently part of a redundant configuration and you want to use it in another configuration, you can use Dell SAS RAID Storage Manager commands to remove the disk drive from the first configuration for this purpose. When you do this, all data on that drive is lost.
NOTE: Certain operations, such as creating a new virtual disk, cannot be performed if pinned cache exists. In addition, if you reboot your server, the operating system will not start as long as the pinned cache exists. Messages notify you that you cannot perform the procedure until you either delet the pinned cache or import the virtual disks with the pinned cache.
Upgrading the Firmware Dell SAS RAID Storage Manager enables you to easily upgrade the controller firmware. The latest firmware packages are available at support.dell.com. The images used for the update are contained in this package. To upgrade the firmware, follow these steps: 1 In the left panel of the Dell SAS RAID Storage Manager window, click on the icon of the Dell controller you need to upgrade. 2 In the right panel, click the Operations tab and select Flash Firmware. 3 Click Go.
Maintaining and Managing Storage Configurations
Troubleshooting To get help installing Dell SAS RAID Storage Manager on your Dell™ PERC 5/i, SAS 5/iR, PERC 6/i, or SAS 6/iR system, you can contact your Dell Technical Service representative or access the Dell Support website at support.dell.com. Pinned Cache State If a virtual disk becomes offline or is deleted for any reason, the firmware preserves the dirty cache from the virtual disk.
Windows Installation Error Messages The Microsoft Installer might display error messages during the installation process when you are installing Dell SAS RAID Storage Manager on a Dell system running under the Microsoft Windows operating system. The error messages are self-explanatory. If you need more information about these messages, see the list of Installer error messages on the Microsoft Developers Network (MSDN) website at this address: http://msdn.microsoft.com/library/default.
Other Dell SAS RAID Storage Manager Messages Table 7-2 lists other messages generated by Dell SAS RAID Storage Manager and explains what should be done to respond to them. Table 7-2. Dell SAS RAID Storage Manager Messages Message Meaning Action Event ID 0X27 This means that patrol read is disabled. This message displays if you try to start patrol read when it is not enabled. Change the patrol read mode to Auto or Manual from Disabled. See Running a Patrol Read in Chapter 5 for detailed instructio ns.
Table 7-2. Dell SAS RAID Storage Manager Messages (continued) Message Meaning Guided Configuration Failed! Dell SAS RAID Storage Close the Configuration Wizard and Manager could not proceed then retry. with guided configuration. This might occur because the underlying hardware resources were changed during the configuration: for example, a drive was removed.
Table 7-2. Dell SAS RAID Storage Manager Messages (continued) Message Meaning Action Storelib Initialization failed StoreLib (the library used by Check the knowledgebase articles Dell SAS RAID Storage on support.dell.com. Manager) could not be initialized on the system. No SAS hardware or driver is present on the system. No Storage Controller Found! No controller could be found on the system. No SAS hardware or driver is present on the system.
Table 7-2. Dell SAS RAID Storage Manager Messages (continued) Message Meaning Action Cannot create Virtual Disk: Invalid input parameters for creating Virtual Disk. You have entered some parameters that are not valid for the virtual disk. Be sure that all the virtual disk parameters are valid, and then retry creating the virtual disk. The drive is not in a state to perform. The physical drive does not This functionality is not supported. support this command.
Table 7-2. Dell SAS RAID Storage Manager Messages (continued) Message Meaning Action Clear Foreign Config failed! The Clear Foreign Config Use the controller BIOS operation has failed with an configuration utility to execute this error. task. (See the SAS controller user’s guide for further instructions.) This is a non-recoverable operation, so be sure that you want to do this before continuing. No Servers found! Dell SAS RAID Storage Manager did not find any servers to manage.
Troubleshooting
Events and Messages This appendix lists the Dell SAS RAID Storage Manager events that might appear in the event log. Dell SAS RAID Storage Manager monitors the activity and performance of all controllers in the workstation and the devices attached to them. When an event occurs, such as the start of an initialization, an event message appears in the log at the bottom of the Dell SAS RAID Storage Manager window.
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Table A-2. Event Messages (continued) Number Type Event Text 0x00d1 Info BBU Retention test was initiated on previous boot 0x00d2 Info BBU Retention test passed 0x00d3 Caution BBU Retention test failed! 0x00d4 Info NVRAM Retention test was initiated on previous boot 0x00d5 Info NVRAM Retention test passed 0x00d6 Caution NVRAM Retention test failed! 0x00d7 Info %s test completed %d passes successfully 0x00d8 Caution %s test FAILED on %d pass.
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Events and Messages
Glossary Access Policy A virtual disk property indicating what kind of access is allowed for this virtual disk. The possible values are Read/Write, Read Only, or Blocked. adapter A device that enables a computer system to access peripheral devices by converting the protocol of one bus or interface to another. An adapter can also provide specialized function. For example, a RAID controller is a type of adapter that provides RAID functions. Adapters can reside on the system board or be an add-in card.
BGI Rate A controller property indicating the rate at which the background initialization of virtual disks will be carried out. BIOS Basic Input/Output System. The computer BIOS is 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. cache Fast memory that holds recently accessed data.
Coercion Mode A controller property indicating the size to which disk drives of nominally identical capacity are coerced (forced) in order to make them usable in a storage configuration. consistency check An operation that verifies that all stripes in a virtual disk with a redundant RAID level are consistent and that automatically fixes any errors. For RAID 1 disk groups, this operation verifies correct mirrored data for each stripe.
device driver Software that allows the operating system to control a device such as a printer. Many devices do not work properly if the correct driver is not installed in the computer. Device ID A controller or physical disk property indicating the manufacturer-assigned device ID. Device Port Count A controller property indicating the number of ports on the controller.
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 set of physical disks that you install in a computer system.
hotspare A standby physical disk that can automatically replace a failed physical disk in a virtual disk and prevent data from being lost. A hotspare can be dedicated to a single redundant disk group or it can be part of the global hotspare pool for all disk groups controlled by the controller. When a physical disk fails, Dell SAS RAID Storage Manager automatically uses a hotspare to replace it and then rebuilds the data from the failed physical disk to the hotspare.
mirroring The process of providing complete data redundancy with two physical disks by maintaining an exact copy of one 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. Name A virtual disk property indicating the user-assigned name of the virtual disk.
patrol read rate The user-defined rate at which patrol read operations are run on a computer system. physical disk (PD) A non-volatile, randomly addressable device for storing data. Physical disks are rewritable and commonly referred to as disk drives. Physical Drive State A physical drive property indicating the status of the drive.
Product Info A physical disk 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 disk drives that provide high performance by increasing the number of disks used for saving and accessing data. A RAID disk group improves input/output (I/O) performance and data availability.
RAID 6 RAID 6 uses data striping and dual parity across four or more disks (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 disk drives. The PERC 6/i controller supports RAID 6. RAID 10 RAID 10, a combination of RAID 0 and RAID 1, uses data striping across mirrored spans. It provides high data throughput and complete data redundancy.
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, read-ahead capability is disabled.
Revision Level A physical disk property that indicates the revision level of the disk’s firmware. SAS 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.
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 physical disks connected to the controller. If the error count reaches a certain level, a physical disk will be marked as Failed. Vendor ID A controller property indicating the vendor-assigned ID number of the controller.
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 disk subsystem has received all the data and has completed the write transaction to the disk.
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