Overview of Hot Spares

A hot spare is a component that is running (but not being used) that can be substituted for a broken component in a submirror of a two- or three-way mirror or a RAID metadevice. Failed components in a one-way mirror cannot be replaced by a hot spare, since no other copy of the data is available.

A hot spare is to a mirror or RAID metadevice what a spare tire is to a car. A spare is meant to quickly replace a flat tire, thus increasing the availability of your car. A spare tire is a temporary fix that is made with the intention that the flat tire will be repaired or replaced with a new one and the spare will be returned to the trunk.

This is exactly how hot spares should be treated. They are not intended to be used as permanent fixes when a component has failed. They are temporary fixes that can be used until a failed component is either repaired or replaced.

Components designated as hot spares cannot be used to hold replicas. They must remain ready for immediate use in the event of a component failure.

Hot Spare Conditions to Avoid

Avoid these three conditions:

• Associating hot spares of the wrong size with submirrors or RAIDs. This condition occurs when hot spare pools are defined and associated with a submirror and none of the hot spares in the hot spare pool are the same size or larger than the smallest component in the submirror. This would occur, for example, when 669-Mbyte disk drives make up the hot spare pool that is associated with a submirror that is made up of a 1-Gbyte drive.
• Having all hot spares within the hot spare pool in use. When the administrator notices that all hot spares are in use, immediate action is required. There are two possible solutions when this occurs. The first is to add additional hot spares. The second is to repair some of the components that have been replaced with hot spares. If all hot spares are in use and a submirror or RAID fails due to errors, that portion of the mirror will no longer be replicated.
• Assigning a hot spare pool to a submirror in a one-way mirror. This would provide no protection against unavailable data.

Defining Hot Spares

After a hot spare pool is defined, it can be associated with one or more submirror or RAID metadevices. Hot spare pools are named hspnnn where nnn is a number in the range 000-999. A metadevice cannot be configured as a hot spare.

A hot spare can be used in one or more hot spare pools, thus allowing for the maximum amount of security from the minimum number of components. DiskSuite looks for the first available hot spare from the designated pool when errors are reported.

With DiskSuite Tool, you can also define empty hot spare pools so hot spares can be added when they become available.

The procedure for defining hot spare pools is provided below.

1. Start DiskSuite Tool.

# metatool

2. Open a Hot Spare Pool template on the Metadevice Editor canvas.

   Click on the Hot Spare Pool template. An unassigned and uncommitted Hot Spare Pool template is opened on the Metadevice Editor canvas. When you point to the template, the message line displays the hot spare pool name and the status.

3. Open the Slice Browser.

   Click on Slices on the button panel.

4. Select slices for the Hot Spare Pool template.

   Locate the appropriate slices to be assigned to the hot spare pool. The slices should be attached to different controllers. Click on the first slice that will be assigned to the Hot Spare Pool, hold down the Control key, and click on the second slice.

5. Drag the slices into the Hot Spare Pool template.

   Point to one of the selected slices in the Slice Browser. Press the middle button and drag the slices to the Hot Spare Pool template.

6. Commit the Hot Spare Pool template.

   Click on the top rectangle of the hot spare pool template. Then click on the Commit button.

Associating Hot Spare Pools

After a hot spare pool has been defined it is ready to be associated with a mirror or RAID configuration. When a component failure occurs, DiskSuite searches through the list of hot spares in the assigned pool and selects the first available component that is of equal or greater disk capacity than the failed slice it will replace.

If a hot spare of adequate size is found, the hot spare's state changes to in-use and a resync operation is automatically performed. The resync operation brings the hot spare data into sync with the other submirror or the rest of the RAID metadevice.

If a component of adequate size is not found in the list of hot spares, the submirror that failed is considered to be in an error condition and that portion of the submirror no longer replicates the data or, in the case of RAID, the data redundancy is no longer available.

The procedure for associating a hot spare pool with a mirror follows. The same procedure would be used for a RAID metadevice.

1. Open a Mirror and Hot Spare Pool.

   Scroll through the device list on the Metadevice Editor window and find the Mirror and the Hot Spare Pool. Point to each and double-click. In this example, Mirror d5 and Hot Spare Pool hsp002 are used.

2. Drag the Hot Spare Pool template into the submirror.

   Point to the upper region of the Hot Spare Pool, press the middle button and drag the object to the top of the d4 submirror.

The Hot Spare Pool is associated with the d3 submirror using the same procedure. After the Hot Spare Pool is associated with the second submirror, the Use field changes from None to Shared by 2.

3. Commit the mirror

   Click inside the top rectangle of the d5 Mirror. Then click on the Commit button.

Manipulating Hot Spare Pools

DiskSuite Tool enables you to dynamically add, delete, replace, and enable hot spares within existing hot spare pools. You can perform the following functions on hot spare pools:

• Add hot spares to hot spare pools
• Delete hot spares from hot spare pools
• Replace hot spares in hot spare pools
• Enable hot spares
• Check the status of hot spares

Adding Hot Spares

You can add a hot spare to one or more hot spare pools. When a hot spare is added, the existing order of the hot spares already in the pool is preserved. The new hot spare is added at the end of list of hot spares in the hot spare pool that is specified.

The following example shows how to add a slice to a hot spare pool (hsp001).

1. Select an existing Hot Spare Pool object.

   Scroll through the device list on the Metadevice Editor window and open the hot spare pool that will have the new hot spare added. In this example, Hot Spare Pool hsp001 is used.

2. Open the Slice Browser.

   Click on Slices on the button panel.

3. Select a slice to be added to the Hot Spare Pool template.

   Locate a slice of the same or greater size than the slice that is already in the Hot Spare Pool. To select a slice, point to it and click. In this example, c2t2d0s0 was selected because it is the same size as the other slices in hsp001.

4. Drag the slice into the Hot Spare Pool object.

   Point to the slice, press the middle button, and drag the cursor to the Hot Spare Pool.

5. Commit the Hot Spare Pool object.

   Click on the top rectangle of the Hot Spare Pool object. Then click on the Commit button.

Deleting Hot Spares

Hot spares can be deleted from any or all the hot spare pools to which they have been associated. DiskSuite Tool will not allow a hot spare to be deleted if it is in use.

When a hot spare is deleted from a hot spare pool, the positions of the remaining hot spares change to reflect the new position. For example, if the second of three hot spares in a hot spare pool is deleted, the third hot spare moves to the second position.

Use the following procedure to delete a hot spare from a hot spare pool.

1. Open the Hot Spare Pool object.

   Scroll through the device list in the Metadevice Editor window and double-click on the Hot Spare Pool from which a hot spare will be deleted. In this example, Hot Spare Pool hsp001 is used.

2. Remove the hot spare from the Hot Spare Pool object.

   Point to the slice (hot spare) that is being removed from the Hot Spare Pool, press the middle button, and drag the slice onto the Metadevice Editor canvas. In this example, hot spare c1t1d0s6 is being removed.

3. Commit the Spare Pool object.

   Click inside the top rectangle of the Hot Spare Pool object. Then click on Commit on the button panel.

Replacing Hot Spares

Hot spares can be replaced in any or all the hot spare pools to which they have been associated. However, hot spares that are in use cannot be replaced by other hot spares.

The order of hot spares in the hot spare pools is not changed when a replacement occurs.

Use the following procedure to replace a hot spare in a hot spare pool.

1. Open the Hot Spare Pool object.

   Scroll through the device list on the Metadevice Editor window and open the Hot Spare Pool object in which you want to replace a hot spare (slice). In this example, hot spare pool hsp001 is used. The slice being replaced is c2t2d0s0.

2. Open the Slice Browser.

   Click on Slices on the button panel.

3. Select a replacement slice.

   Locate an appropriate slice for replacement of slice c2t2d0s0. The replacement slice should be as large as the slice it is replacing. In this example, c2t2d0s1 is selected.

4. Replace the slice in the Hot Spare Pool.

   Point to the replacement slice (c2t2d0s1), press the middle button, and drag the cursor to the rectangle that contains the slice to be replaced (c2t2d0s0).

5. Commit the Hot Spare Pool.

   Click inside the top rectangle of the Hot Spare Pool object. Then click on Commit on the button panel.

Enabling Hot Spares

When a hot spare that has been placed in the broken state is repaired, you can make it available using DiskSuite Tool.

Use the following procedure to enable a hot spare after it has been repaired.

1. Open the Hot Spare Pool object.

   Scroll through the device list on the Metadevice Editor window and open the Hot Spare Pool object with the repaired or replaced slice. Point to the Hot Spare Pool and double-click. In this example, hot spare pool hsp002 is opened.

2. Open the Hot Spare Pool Information window.

   Point to the top rectangle of the Hot Spare Pool template and press the right button. Select Info from the menu.

3. Select and enable the hot spare slice that has been replaced.

   Click on the slice. Then click on Enable. In this example, c6t4d2s0 was selected and enabled.

4. Commit the Hot Spare Pool.

   Click inside the top rectangle of the Hot Spare Pool object. Then click on Commit on the button panel.

Changing the Associated Hot Spare Pool

Each hot spare pool can be associated with one or more submirrors or RAID metadevices. The association can be made and changed using DiskSuite Tool. This can be performed while the system is running, if none of the hot spares in the hot spare pool is being used by the submirror or RAID.

In the following example, the hot spare pool hsp001, is currently associated with Concat/Stripe d16 in the mirror d12. This following procedure changes the hot spare pool association to hsp000.

1. Open the d12 Mirror.

   Point to the d12 Mirror in the device list and double-click.

2. Open the Hot Spare Pool.

   Double-click on the hsp000 Hot Spare Pool in the device list.

3. Replace hsp001 with hsp000.

   Point to hsp000, press the middle button, and drag the object to the rectangle that contains hsp001 in the d16 submirror.

4. Commit the d12 mirror.

   Click inside the top rectangle of the d12 Mirror. Then click on the Commit button.

Hot Spare Information Window

The Hot Spare Information window allows you to view and modify the attributes and components of a specific hot spare. Figure 7-1 shows the Hot Spare Information window. There are three ways to display the Hot Spare Information window:

• Point to the hot spare pool in the Hot Spare Pool Browser and double-click. The hot spare pool object is opened on the Metadevice Editor's canvas and the Hot Spare Information window is displayed.
• If the Hot Spare Pool object is on the Metadevice Editor's canvas, point inside the top of the Hot Spare Pool rectangle and bring up the Hot Spare Pool menu. Select the Info choice.

• Double-click on a Hot Spare Pool object on the Metadevice Editor's canvas.

Figure 7-1

The Hot Spare Pool object must be committed before the changes take effect.

Table 7-1 lists the functionality associated with the regions of the Hot Spare Pool Information window.

Table 7-1

Field	Functions
Device name	The name of the Hot Spare Pool.
Status	Description of the Hot Spare Pool's status. See "Checking the Status of Hot Spares" on page 191" for a description of the values that appear in this region.
Smallest	The size of the smallest slice in the Hot Spare Pool.
Largest	The size of the largest slice in the Hot Spare Pool.
Associated With	A scrolling list that displays the device names, types, and status of all metadevices associated with the Hot Spare Pool. To display information about the object either click on the object then click on Info or point to the object and double-click.
Info	Displays the Concatenation Information window for the selected (highlighted) Concat/Stripe in the Associated With region.
Hot Spare manipulation region	Contains a list of all the slices included in the Hot Spare Pool. New slices can be added. Existing slices can be manipulated. The functions of the buttons include: Show Hot Spare - A toggle switch that shows or hides the bottom portion of the window. List of slices - A scrolling list of the slices included in the Hot Spare Pool. Enable - Enables selected slices that are disabled. Remove - Removes the selected slices from the Hot Spare Pool. Info - Displays the Slice Information window for the selected (highlighted) slice. Slice - Specifies a new slice to attach or replace the selected slice. Attach - Attaches the slice specified in the Slice field to the Hot Spare Pool. This button is active only when a slice name has been entered in the field. Replace - Replaces the selected spare slice with the slice entered in the field. This button is active only when a slice name has been entered in the field and a slice is selected on the list of slices.

Checking the Status of Hot Spares

There are three ways to check the status of hot spare pools using DiskSuite Tool. The methods are:

• Open the hot spare pool template if it is in the device list and check the Status field.
• Bring up the Hot Spare Pool 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 Hot Spare Pools use the status keywords explained in Table 7-2.

Table 7-2

Keyword	Meaning
OK	The hot spares are running and ready to accept data, but are not currently being written to or read from.
In-use	Hot spares are currently being written to and read from.
Attention	There is a problem with a hot spare or the Hot Spare Pool, but there is no immediate danger of losing data. This status is also displayed if there are no hot spares in the Hot Spare Pool or all the hot spares are in use or any are broken.