Administrator's Guide

RAID

The redundant array of independent disks (RAID) configuration allows you to dynamically manage the logical drives. A logical drive is a unit of virtual storage that is made available to the network. Logical drives consist of multiple physical disks combined using RAID level 0, 1, 1E, 5 or 5E technology. A physical disk cannot hold any user data unless it belongs to a logical drive.

The IBM IP Storage Model 200 supports up to 48 physical disks in a fully configured system. The minimum number of logical drives is one, and the maximum number is eight. (If any logical drive has a RAID configuration of 5E, then the maximum number of logical drives is seven.) Each logical drive can have a maximum of 16 physical disks, although a maximum of eight is recommended.

The Model 100 supports up to 6 physical disks.

The following types of disks are shown:

Physical disks
A disk that has not been assigned as a hot-spare, standby hot-spare, or to a logical drive.

Hot-spare disks
A disk that is not part of a logical drive but can be mapped to a logical drive if one of the logical drive's disks goes offline. The logical drive runs in a degraded, or exposed, condition until all data on the new disk is regenerated.

A hot-spare disk can also be defined as a standby hot-spare disk. A standby hot-spare can be mapped to a logical drive if no suitable hot-spare disk is available.

Except for RAID 0, a single disk failure can be recovered by replacing the failed disk. No configuration changes are necessary. If a hot-spare disk is available, it is automatically used to replace the failed disk. Data is automatically rebuilt for the hot-spare disk. If a hot-spare disk is not available, data is rebuilt when the failed disk is replaced with a new disk.

Logical drives
A disk that has been assigned to a logical drive. These disks are displayed under the logical drive in the RAID Configuration tree.

The RAID panel is divided into two subpanels: the RAID Configuration tree containing a graphical representation of the RAID controller, logical drives, and physical disks in the system and the Properties table that shows the information about the selected component.

Refreshing the configuration

The RAID configuration panel is refreshed each time the panel is opened and after each task. It is not automatically updated after a given period of time. It is recommended that you refresh this panel after an extended period of time.

To refresh the RAID configuration displayed on the Administrative Console:

  1. Click Storage --> RAID.
    Note:Displaying this pane for the first time may take several minutes, depending on your network-connection speed.
  2. Click Controller 1 to highlight it.
  3. Right-click Controller 1.
  4. Click Refresh the configuration from the pop-up menu.

Scanning for physical disks

When you add or remove disks, you must update the RAID configuration by scanning the appliance for current physical disks.
Note:Physical disks that are part of a logical drive must not be disrupted by removal or replacement. Adding, removing, and replacing physical disks must be restricted to free disks.

To scan the appliance for new and removed disks in the Ready state using the Administrative Console:

  1. Click Storage --> RAID.
    Note:Displaying this pane for the first time may take several minutes, depending on your network-connection speed.
  2. Click Controller 1 to highlight it.
  3. Right-click Controller 1.
  4. Click Scan for ready disks from the pop-up menu.
  5. Click Scan to scan for disks. When scanning is complete, the dialog box reports the number of new and removed disks found.
  6. Click Close. The dialog box closes, and any new disks are moved to the Physical disks folder in the RAID Configuration tree.

Creating a logical drive

You can create a maximum of eight logical drives on one appliance.

To create a logical drive using the Administrative Console:

  1. Click Storage --> RAID.
    Note:Displaying this pane for the first time may take several minutes, depending on your network-connection speed.
  2. Click Controller 1 to highlight it.
  3. Right-click Controller 1.
  4. Click Add logical drive from the pop-up menu.
  5. Select the RAID level from the RAID level drop-down list. You can choose one of the following levels:

    RAID 0
    Stripes the data across all physical disks in the logical drive. This level offers substantial speed enhancements, but provides no data redundancy. It provides the largest capacity of the RAID levels because no room is taken for redundant data or data-parity storage.

    RAID level 0 requires a minimum of one physical disk, and supports a maximum of 16 physical disks. If you have a logical drive that contains only one physical disk, you can assign only RAID level 0 to that logical drive.

    This level is recommended for data stores primarily used for sequential data operations where data stores require no redundancy (for example, program-file repositories and daily backups).

    RAID 1
    Provides data redundancy using disk mirroring. The first half of a stripe is the original data; the second half of a stripe is a mirror (copy) of the data that is written to another disk in the RAID level 1 logical drive. If one physical disk fails, the ServeRAID(TM) controller switches read and write requests to the remaining functional disk in the RAID level 1 logical drive.

    RAID level 1 requires two physical disks. If you have three or more physical disks in the logical drive, you cannot select RAID level 1. You can, however, select RAID level 1 Enhanced (RAID level 1E).

    This level is recommended for high-performance and write-intensive random-access applications (for example, database applications).

    RAID 1E
    Combines mirroring with data striping. This RAID level stripes data and copies the data across all of the disks in the logical drive. If one of the physical disks fails, the ServeRAID controller switches read and write requests to the remaining functional drives in the RAID level 1E logical drive.

    RAID level 1E requires a minimum of three physical disks and supports a maximum of 16.

    RAID 5
    Stripes data and parity across all physical disks in the logical drive. The capacity of the logical drive is reduced by one physical disk, for data-parity storage.

    RAID level 5 requires a minimum of three physical disks and supports a maximum of 16.

    RAID 5E
    Is the same as RAID level 5 with a built-in hot-spare disk. Like RAID level 5, RAID level 5E stripes data and parity across all physical disks in the logical drive. The capacity of the logical drive is reduced by two physical disks: one for data-parity storage and one for hot-spare. This RAID level is more efficient than RAID level 5 (three physical disks) with an idle hot-spare. This spare cannot be shared with the other logical drives.

    RAID level 5 requires a minimum of four physical disks and supports a maximum of 16. You can have a maximum of seven RAID level 5E logical drives.

  6. Select the write-cache method from the Write cache method drop-down list. You can choose one of the following values:
  7. Add physical disks to the logical drive:
    1. Select one or more physical disks that you want to add to the logical drive from the Available disks list.
    2. Click >>> to add the selected disks to the Selected Disks list.

    The size of the logical drive displayed below the Selected Disks list is calculated each time you move a disk from either list.
    Note:Depending on your choice of RAID levels, there might be restrictions on the number of physical disks that can be used to create the logical drive. The Administrative Console warns you of invalid assignments. You can assign a maximum of 16 physical disks to one logical drive.

  8. Remove a physical disk from the selected list.
    1. Select one or more physical disks you want to remove from the Selected Disks list.
    2. Click <<< to move the selected disks back to the Available disks list.
  9. Click Add. The new logical drive appears in the RAID Configuration tree with the assigned disks nested beneath it.

Removing a logical drive

Note:If virtual logical units (VLUNs) are assigned on the selected logical drive, you are not able to remove the logical drive. All VLUNs must be removed before a logical drive can be deleted (see Removing all virtual logical units from a logical drive).

To remove a logical drive using the Administrative Console:

  1. Click Storage --> RAID.
    Note:Displaying the RAID panel for the first time may take several minutes, depending on your network-connection speed.
  2. Click the logical drive you want to delete.
  3. Right-click the logical drive.
  4. Click Remove drive from the pop-up menu.
  5. Click Remove to delete the selected logical drive. The logical drive is deleted and the disks previously associated with the logical drive are moved under Physical disks in the RAID Configuration tree.

Resizing a logical drive

You can increase the size of a logical drive by adding new physical disks to it. Note that you cannot change the RAID level of an existing logical drive.

Attention: Modifying the size of a logical drive can take several hours to complete. You cannot perform many RAID-controller tasks (such as adding and removing a logical drive) during an expansion operation. These tasks are disabled until the expansion is completed.

To add physical disks to or remove physical disks from a logical drive using the Administrative Console:

  1. Click Storage --> RAID.
    Note:Displaying the RAID panel for the first time may take several minutes, depending on your network-connection speed.
  2. Click the logical drive you want to expand.
  3. Right-click the logical drive.
  4. Click Expand drive from the pop-up menu.
  5. Add physical disks to the logical drive:
    1. Select one to three physical disks that you want to add to the logical drive from the Available disks list. You can add up to three new physical disks to an existing logical drive.
    2. Click >>> to add the selected disks to the Expanded drive list.

    The size of the logical drive displayed below the Expanded Disks list is calculated each time you move a disk from either list.

  6. Remove a physical disk from the Expanded drive list:
    1. Select one or more physical disks you want to remove from the Expanded drive list.
    2. Click <<< to move the selected disks back to the Available disks list.
  7. Click Expand to expand the selected logical drive.
  8. Wait for the expansion operation to complete. A progress bar appears below the RAID configuration tree to indicate the progress of the operation.

Defining a disk as hot-spare

To create a hot-spare disk using the Administrative Console:

  1. Click Storage --> RAID.
    Note:Displaying the RAID panel for the first time may take several minutes, depending on your network-connection speed.
  2. Click the physical or standby hot-spare disk you want to define as hot spare.
  3. Right-click on the disk.
  4. Click Create hot-spare from the pop-up menu. The selected disk is moved to the Hot-spares folder in the RAID Configuration tree, and its state shown in the Properties table is changed to "Hot-Spare (HSP)."

Defining a disk as standby hot-spare

To create a standby hot-spare disk using the Administrative Console:

  1. Click Storage --> RAID.
    Note:Displaying the RAID panel for the first time may take several minutes, depending on your network-connection speed.
  2. Click the physical or hot-spare disk you want to define as hot spare.
  3. Right-click the disk.
  4. Click Create standby hot-spare from the pop-up menu. The selected disk is moved to the Hot-spares folder in the RAID Configuration tree, and its state shown in the Properties table is changed to "Standby Hot-Spare (SHS)."

Freeing a hot-spare or standby hot-spare disk

To make a hot-spare or standby hot-spare disk available using the Administrative Console:

  1. Click Storage --> RAID.
    Note:Displaying the RAID panel for the first time may take several minutes, depending on your network-connection speed.
  2. Click the hot-spare or standby hot-spare disk you want to free.
    Note:You can determine whether the disk is a hot-spare disk or a standby hot-spare disk viewing the state shown in the Properties table.
  3. Right-click the disk.
  4. Click Remove hot-spare or Remove standby hot-spare from the pop-up menu. The selected disk is moved under Physical disks in the RAID Configuration tree, and its state shown in the Properties table is changed to "Ready (RDY)."

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