RAID Overview

DiskSuite supports level 5 RAID devices. A RAID configuration allows you to recover from a single disk failure. It can also be more cost effective than mirroring disks.

RAID metadevices must be comprised of three or more physical slices. Each slice is referred to as a component. A RAID metadevice can be grown by concatenating additional slices to the metadevice.

RAID level 5 includes multiple physical slices used to simulate a single large slice. A single sector on one of these physical slices contains either a sector's worth of data, or parity information relating to the data on the same sector of all other slices in the array.

In order to eliminate a parity slice as a bottleneck, no one physical slice will hold all of the parity information; it will be placed on different slices for different sectors.

---

Caution - Do not attempt to create a RAID device with slices that contain an existing file system. The data on the slices will be erased when the RAID goes through a resync.

---

The advantages of a RAID level 5 configuration are:

• It can recover from a disk failure.
• It is more cost effective than mirroring disks.

DiskSuite Tool automatically resyncs RAID metadevices when components are replaced or new components are added.

Operation of RAID

The following operations are supported for RAID metadevices using DiskSuite Tool:

• Configuring and defining RAID metadevices
• Concatenating new components to existing RAID metadevices
• Allocating hot spare pools to RAID metadevices to provide component backup in the event of original component failures
• Replacing failed components or in-use hot spare components with a new component
• Viewing the status of RAID metadevices
• Clearing RAID metadevices

Each of these operations is discussed in more detail in the following sections.

Hardware and Software Considerations

There are both hardware and software considerations that affect RAID metadevices. For a detailed discussion of all hardware and software considerations, refer to Chapter 9 of the Solstice DiskSuite 4.0 Administration Guide.

Creating RAID Metadevices

This subsection describes how to create a RAID metadevice using DiskSuite Tool. In the example used, the RAID metadevice will contain three slices of equal size. An interlace value of 32 Kbytes will be set.

The following example shows how to create a RAID metadevice.

1. Start DiskSuite Tool.

# metatool

2. Open a RAID template on the Metadevice Editor canvas.

   Click on the RAID template. An unassigned and uncommitted RAID template is opened on the Metadevice Editor canvas. When you point to the template, the message line displays the metadevice name, size, use, and status.

3. Open the Slice Browser.

   Click on Slices on the button panel.

4. Select the first slice for the RAID device.

   Scroll through the list of slices and select the first slice for the RAID device.

5. Drag the slice into the RAID template.

   Point to the slice, press the middle button, and drag the cursor to the RAID template. The size is represented as none, because the size is not known until there are at least three slices in the RAID metadevice.

6. Drag additional slices into the RAID template.

   Scroll through the Slice Browser and locate additional slices for the RAID device. The slices should be the same size as the initial slice and ideally attached to different controllers. In this example, slice c6t4d3s0 was the first slice. The second and third slices are c7t1d0s0 and c5t5d4s0. All the slices are 989 Mbytes. However, the Size field of the RAID template reports the size as 1.92 Gbytes because the equivalent capacity of one disk is used for parity.

7. Optionally change the interlace size.

   By default the interlace value of the RAID is set to 16 Kbytes. To change the interlace value, point to the top of the RAID template rectangle, press the right button, and select Info from the menu.

The RAID Information window is displayed, showing information about the RAID device.To change the interlace value, point to the Custom button and click. Enter the new value and click on Attach.

For more about the RAID Information window, see page 214.

8. Commit the RAID metadevice.

   Click inside the top rectangle of the d9 RAID metadevice. Then click on Commit on the button panel.

Reconfiguring RAID Metadevices

Reconfiguration of a RAID metadevice includes the following operations:

• Concatenating additional components to the RAID metadevice
• Assigning a hot spare pool to the metadevice to provide a backup in the event that errors are encountered on any of the components of the metadevice
• Replacing components (error or non-errored)

Instructions for performing each of these reconfiguration options are provided in the following subsections.

Concatenating Components

You can concatenate a component to a RAID metadevice to expand the device's capacity.

When a slice is added to the RAID metadevice, the slice becomes a concatenation to the initial metadevice. The new slice will not contain RAID level 5 parity information. But the data on the new slice will be protected by the parity that already existed in the metadevice.

---

Note - After the slice is added and the RAID metadevice is committed, the slice cannot be removed. However, the slice can be replaced by a slice of equal or greater size.

---

The following example shows how to add a slice to an existing RAID metadevice. The added slice will be a single concatenated component.

1. Start DiskSuite Tool.

# metatool

2. Open the RAID metadevice object on the Metadevice Editor canvas.

   Scroll through the device list on the Metadevice Editor to find the RAID metadevice object that will receive an additional slice. Point to the device and double-click the left button.

3. Open the Slice Browser.

   Click on Slices on the button panel.

4. Select a slice to be added to the RAID metadevice.

   Scroll through the list of slices and select a slice that will be added to the metadevice. The slice must be at least as large as the smallest slice in the metadevice. In this example, c4t5d3s0 was selected because it is the same size as the other slices and is connected to a different controller.

5. Drag the slice into the RAID metadevice.

   Point to the c4t5d3s0 slice, press the middle button, and drag the slice to the top rectangle of the RAID metadevice.

6. Commit the RAID metadevice.

   Click on the top rectangle of the d9 RAID metadevice. Then click on Commit on the button panel.

Assigning a Hot Spare Pool

Hot spare pools may be allocated, deallocated, or reassigned at any time unless a component in the hot spare pool is being used to replace an errored component in the RAID metadevice.

After the hot spare pool has been assigned to the metadevice, any failed components will be replaced by the first available appropriately sized component in the hot spare pool.

The following steps describe how to assign a hot spare pool to a RAID metadevice.

1. Start DiskSuite Tool.

# metatool

2. Open the d9 RAID metadevice object on the Metadevice Editor canvas. Scroll through the device list on the Metadevice Editor to find the RAID metadevice object that will be associated with a hot spare pool. Once located, point to the device and double-click the left button.

3. Open the Hot Spare Pool Browser.

   Point to the Browse menu on the menu bar of the Metadevice Editor window, press the right button, and select Hot Spare Pools.

4. Select a hot spare pool object.

   Scroll through the list of Hot Spare Pool objects and select the one that will be assigned to the RAID metadevice. The hot spare pool must have slices the same size or larger than the slices in the RAID metadevice. Ideally, the Hot Spare Pool will contain hot spares that are on a different controller than the slices in the RAID metadevice.

5. Assign the Hot Spare Pool object to the RAID metadevice.

   Point to the Hot Spare Pool object, press the middle button, and drag the object to the top rectangle of the RAID metadevice.

6. Commit the RAID metadevice.

   Click inside the top rectangle of the RAID metadevice. Then click on Commit on the button panel.

Replacing Components

When an I/O error is detected on a component of a RAID metadevice, no further actions will be performed on that component. You should replace the component or perform some other type of error recovery to return the state of the RAID metadevice to non-errored. This reduces the possibility of lost data.

---

Caution - Replacing an errored component when multiple components are in error may cause data to be fabricated. The integrity of the data in this instance is questionable.

---

The following example shows how to replace an errored slice in a RAID metadevice.

During component replacement, data for the errored component will be recovered from a hot spare component or from the available, non-errored, components. This is possible due to the parity segments that are generated during normal I/O operation.

The following steps show how to replace a component in a RAID metadevice.

1. Start DiskSuite Tool.

# metatool

2. Open the RAID metadevice object on the Metadevice Editor canvas.

   Scroll through the device list on the Metadevice Editor and find the RAID metadevice object that will receive a replacement slice. Point to the RAID metadevice and double-click the left button.

3. Open the Slice Browser.

   Click on Slices on the button panel.

4. Select a slice to replace a slice in the RAID metadevice.

   Scroll through the list of slices and select a slice that is at least as large as the smallest component in the RAID metadevice. In this example, c5t1d0s0 was selected. It will replace slice c5t5d4s0 in the RAID metadevice.

5. Replace the slice in the RAID metadevice.

   Point to the selected slice in the Slice Browser, press the middle button, and drag the slice to the rectangle that contains the slice that will be replaced.

6. Commit the RAID metadevice.

   Click inside the top rectangle of the RAID metadevice. Then click on Commit on the button panel.

RAID Information Window

The RAID Information window allows you to view and modify the attributes and components of a specific RAID metadevice. Figure 9-1 shows the RAID Information window. There are three ways to display this window:

• Point to the RAID device in the Metadevice Browser and double-click the left button. The RAID device is opened on the Metadevice Editor's canvas and the RAID Information window is displayed.
• If the RAID metadevice is on the Metadevice Editor's canvas, point inside the top of the rectangle and bring up the RAID menu. Select the Info choice.
• Double-click on a RAID metadevice on the Metadevice Editor's canvas.

Figure 9-1

Once changes are made, the RAID metadevice must be committed before the changes take effect.

Table 9-1 lists the functionality associated with the regions of the RAID Information window.

Table 9-1

Field	Functions
Device name	The metadevice name of the RAID.
Status	Description of the RAID's status. See "Checking the Status of RAID Metadevices" on page 217" for a description of the values that appear in this region.
Size	The size of the usable disk space. This does not include the size set aside for parity.
Use	The use of the RAID, for example, file system or swap. If the use of the RAID is a Trans Log, a Show Trans button is positioned to the right of the field.

Table 9-1

Field	Functions
Hot Spare Pool	This field enables assigning a Hot Spare Pool to the RAID metadevice. It has the following functions: Attach/Detach - Attaches or detaches the specified Hot Spare Pool to the RAID metadevice. Info - Displays the Hot Spare Pool Information window for the specified Hot Spare Pool.
Interlace value region	The default interlace value is 16 Kbytes. To change the interlace value, click on the Custom button and enter the value in the field. The menu button to the right of the field enables you to specify the units used. The values on the menu are Gbytes, Mbytes, Kbytes, and Sectors. The default is Kbytes. After the Custom field is complete, the Attach button is used to assign the interlace value to the RAID. After a RAID is committed, the interlace value cannot be changed.
Slice manipulation region	The following functionality is available in this region: Show Slices - A toggle switch that shows or hides the scrolling list of components at the bottom of the window. Scrolling List - A list of the slices included in the RAID metadevice. The information in this region includes the name of the slice, size, number of state database replicas on the slice and the status. Remove - Removes the selected slices. Enable - Activates the selected slices if they are disabled. Slice - Enables you to specify a new slice to attach to the RAID or replace the selected slice. Attach - Attaches the slice specified in the Slice field to the RAID metadevice. This button is active only when a slice name is entered in the field. Replace - Replaces the selected RAID slice with the slice entered in the Slice field. This button is active only when a slice name has been entered in the field and a slice is selected from the scrolling list. Info - Displays the Slice Information window for the selected (highlighted) slice.

Checking the Status of RAID Metadevices

There are three ways to check the status of RAID metadevices using DiskSuite Tool. The methods are:

• Move the RAID metadevice object from the device list and check the Status field on the object.
• Bring up the RAID metadevice information window and check the Status field.
• Bring up the Problem List window, which is available using the Browse menu on the menu bar of the Metadevice Editor window. If a problem exists, a detailed description of the problem is given.

The Status fields of the RAID metadevice use the status keywords explained in Table 9-2.

Table 9-2

Keyword	Meaning
OK	The RAID metadevice has no errors and is functioning correctly.
Attention	There is a problem with the RAID metadevice, but there is no immediate danger of losing data.
Urgent	There is a problem with the RAID metadevice and you are only one failure away from losing data.
Critical	Data has potentially been corrupted.