Overview

After you create a LUN, you can change its LUN bind parameters, except for its RAID Type, LUN ID, and element size, without unbinding it. You can also change the LUN read caching (prefetch) parameters, which the array automatically sets to their default values when you created the LUN, without unbinding it.

If you want to change the LUN RAID Type or the number or capacity of the disk modules in the LUN, you must unbind the disk modules that comprise it, and then rebind the desired disk modules into another LUN.

This chapter describes how to perform these tasks:

• Change LUN bind parameters that do not require unbinding the LUN
• Change prefetch (read caching) parameters ("Changing prefetch (read caching) parameters")
• Transfer default ownership of a LUN from one SP to another
• Unbind a LUN
• Changing the LUN RAID Type or the number or capacity of disk modules in a LUN

Changing LUN parameters that do not require unbinding

You can change certain LUN Parameters for any LUN except a hot spare without unbinding it, provided the LUN is available to the operating system. These parameters are

• Default SP for any LUN
• Read or write cache state for any LUN except a RAID 3 LUN
• Rebuild time for a RAID 1, RAID 1/0, RAID 3, or RAID 5 LUN
• Verify time for a RAID 1, RAID 1/0, RAID 3, or RAID 5 LUN
• Auto assignment state for any LUN
• Minimum latency reads state for RAID 3 LUNs
• Prefetch (read caching) parameters for any LUN except a RAID 3 LUN

Manuals

Back to Contents Page Configuring a LUN: Dell OpenManage™ Data Supervisor, Event Monitor, and Integrator Installation and Operation Guide Overview

NOTE: Changing the LUN bind parameters does not effect the data stored on the LUN.

This section describes how to change each of these parameters except for the Default SP. Information on changing the Default SP is in the section "Transferring default ownership of a LUN from one SP to another".

Changing any LUN parameter except for the default SP and prefetch parameters

This section describes how to change the following LUN parameters:

• Write cache state
• Read cache state
• Auto assignment state
• Minimal latency reads state
• Rebuild time
• Verify time

You change the above parameters using the options on the LUN menu in the Array Configuration window. The LUN menu contains options for changing each applicable individual parameter and for displaying the Change Bind Parameters window that lets you change all the options. This section describes how to change the parameters either way. The "Bind Parameters" describes the parameters.

You can determine the values of the non-prefetch LUN parameters for a LUN by looking at its LUN Information window.

To use menu options to change individual non-prefetch LUN parameters

A menu option is active only if it is valid for at least one of the selected LUNs.

1. Display the Array Configuration window (see "To display the Array Configuration window").
2. In the LUN selection area of the Array Configuration window, select the LUNs whose parameters you want to change.
3. Change the desired parameter as follows:

Write cache state

1. Select the menu option LUN ® Write Cache State.
2. Select the Enable or Disable option from the list that opens.

A confirmation window opens.

3. In the confirmation window, click the Yes button.



NOTE: The LUN can use write caching only if the array's write cache is enabled. To enable the array's write cache, select the menu option Array ® Write Cache State ® Enable.

Read cache state

1. Select the menu option LUN ® Read Cache State.
2. Select the Enable or Disable option from the list that opens.

A confirmation window opens.

3. In the confirmation window, click the Yes button.



NOTE: The LUN can use read caching only if the read cache for its default SP is enabled. To enable the read cache for SP A, select the menu option Array ® Read Cache State ® SP A ® Enable. To enable the read cache for SP B, select the menu option Array ® Read Cache State ® SP B ® Enable.

Auto assignment state

1. Select the menu option LUN ® Auto Assignment State.
2. Select the Enable or Disable option from the list that opens.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Minimal latency reads state

1. Select the menu option LUN ® Change Minimal Latency Reads State.
2. Select the Enable or Disable option from the list that opens.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Rebuild time

1. Select the menu option LUN ® Change Rebuild Time.
2. Select the desired rebuild time from the list that opens or select Other to enter a time.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Verify time

1. Select the menu option LUN ® Change Verify Time.
2. Select the desired verify time from the list that opens or select Other to enter a time.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

To use the Change Bind Parameters window to change non-prefetch LUN parameters

An option in the Change Bind Parameters window is active only if it is valid for the selected LUNs.

1. Display the Array Configuration window (see "To display the Array Configuration window").
2. In the LUN selection area of the Array Configuration window, select the LUN whose parameters you want to change.
3. Select the menu option LUN ® Change Bind Parameters.

The Change Bind Parameters window for the selected LUN opens, similar to the following sample.

Figure 7-1. Sample Change Bind Parameters window for a RAID 5 LUN



4. If you want to change the read cache state for the LUN, click the Read Cache box.

For example,



A check in the box tells you the read cache is enabled for the LUN.

NOTE: The LUN can use read caching only if the array read cache for the SP that owns it is enabled. To enable the read cache for SP A, select the menu option Array ® Read Cache State ® SP A ® Enable. To enable the read cache for SP B, select the menu option Array ® Read Cache State ® SP B ® Enable.



5. If you want to change the write cache state, click the Write Cache box.

For example,



A check in the box tells you the write cache is enabled for the LUN.

NOTE: The LUN can use write caching only if the array's write cache is enabled. To enable the array's write cache, select the menu option Array ® Write Cache State ® Enable.



6. If you want to change the auto assignment state, click the Auto Assign box.

For example,



A check in the box tells you auto assignment is enabled for the LUN.

7. If you want to change the minimal latency reads state, click the Minimal Latency Reads box.

For example,



A check in the box tells you minimal latency reads are enabled for the LUN.

8. If you want to change the rebuild time, either enter the number of hours in the Rebuild Time field or click the field list button and select the desired rebuild time from the list that opens.

For example,



9. If you want to change the verify time, either enter the number of hours in the Verify Time field or click the field list button and select the desired verify time from the list that opens.

For example,



10. When the bind parameters for the LUN are set as you want, click the OK button.

A confirmation window opens.

11. In the confirmation window, click the Yes button.

Changing prefetch (read caching) parameters

Read-ahead caching (prefetching) lets the SP anticipate the data that an application will request so it can read the data into its read cache before the data is needed. The SP monitors I/O requests to each LUN for sequential reads and, if it finds that any occur, it prefetches data automatically from the LUN. You can define a specific type of prefetch operation for any LUN, except a RAID 3 LUN or hot spare, by specifying the values of the prefetch parameters.

This section describes each of the prefetch parameters and describes how to set the prefetch parameters to their default and non-default values.

Prefetch type

Determines whether to prefetch data of a variable or constant length or to disable prefetching. The default prefetch type is variable length.

Retention

Determines whether prefetched data has equal or favored priority over host requested data when the read cache becomes full. The default retention is favor prefetch.

Disable size

Determines when a read request is so large that prefetching data would not be beneficial; for example, if the amount of requested data is equal to or greater than the size of the read cache. The default disable size is 129 sectors.

Idle count

Determines when prefetching occurs relative to the number of host I/O requests to the LUN. If the number of host I/O requests is greater than the idle count, prefetching occurs; otherwise, prefetching does not occur. We recommend that you leave this parameter set to its default value of 40.

Prefetch size or multiplier

Determines the amount of data prefetched for one host read request. For constant-length prefetching, the prefetch size is the number of blocks to prefetch. For variable-length prefetching, the prefetch multiplier is the amount of data to prefetch relative to the amount of data requested. For example, if the prefetch multiplier is 8, the amount of data to prefetch is 8 times the amount of data requested. The default prefetch multiplier is 4.

Segment size or multiplier

Determines the size of the segments that make up a prefetch operation. An SP reads one segment at a time from the LUN because smaller prefetch requests interfere less with other host requests. For constant-length prefetching, the segment size is the number of blocks of data to prefetch in one read operation from the LUN. For variable-length prefetching, the segment multiplier determines the amount of data to prefetch in one read operation relative to the amount of requested data. For example, if the segment multiplier is 4, the segment size is 4 times the amount of data requested. The default segment multiplier is 4.

Maximum prefetch

Maximum number of blocks to prefetch for variable-length prefetching. The default maximum prefetch size is 512 sectors.

Setting prefetch parameters to default values

Most prefetch parameters have default values. These parameters and their values are

NOTE: We recommend that you use the default values, unless you are certain that the applications that access the LUN will benefit from changing the values.

You set the prefetch parameters for a LUN to their default values using the Prefetch option on the LUN menu in the Array Configuration window. The Prefetch option displays a submenu that contains options for setting the parameters to their default values, for setting individual parameter values and for displaying the Change Prefetch Parameters window that lets you set the parameters to their default values. This section describes how to set the parameters to their default values in either way.

To use the LUN menu option to set prefetch parameters to their default values

1. Display the Array Configuration window (see "To display the Array Configuration window").
2. In the LUN selection area of the Array Configuration window, select the LUNs whose parameters you want to change.
3. Select the menu option LUN ® Prefetch ® Set Default Prefetch Values.

A confirmation window opens.

4. In the confirmation window, click the Yes button.

To use the Change Prefetch Parameters window to set prefetch parameters to their default values

1. Display the Array Configuration window (see "To display the Array Configuration window").
2. In the LUN selection area of the Array Configuration window, select the LUN whose parameters you want to change.
3. Select the menu option LUN ® Prefetch ® Change Prefetch Parameters.

The Change Prefetch Parameters window for the selected LUN opens, similar to the sample.

Figure 7-2. Sample Change Prefetch Parameters window for RAID 5 LUN



4. Click the Use Default Prefetch Values button.

For example,



When you click the button, all other parameters are dimmed to prevent you from changing them.

5. Click the OK button.

A confirmation window opens.

6. In the confirmation window, click the Yes button.

Setting prefetch parameters to non-default values

You can specify the following values for the prefetch parameters

You change the prefetch parameters for a LUN using the options on the LUN menu in the Array Configuration window. The LUN menu contains an options for changing each applicable individual parameter and for displaying the Change Prefetch Parameters window that lets you change all the options. This section describes how to change the parameters either way.

To use menu options to change individual prefetch LUN parameters

1. Display the Array Configuration window (see "To display the Array Configuration window").
2. In the LUN selection area of the Array Configuration window, select the LUNs whose parameters you want to change.
3. Change the desired parameter as follows:

Prefetch Type

1. Select the menu option LUN ® Prefetch ® Set Prefetch Type.
2. Select the None, Constant, or Variable option from the list that opens.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Retention

1. Select the menu option LUN ® Prefetch ® Set Retention.
2. Select the Equal Priority or Favor Prefetch option from the list that opens.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Disable size

1. Select the menu option LUN ® Prefetch ® Set Disable Size.
2. Enter the number of sectors in the window that opens.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Idle count

1. Select the menu option LUN ® Prefetch ® Set Idle Count.
2. Enter the count number in the window that opens, and click the OK button.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Prefetch size

1. Select the menu option LUN ® Prefetch ® Set Prefetch Size.
2. Enter the number of blocks in the window that opens, and click the OK button.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Segment size

1. Select the menu option LUN ® Prefetch ® Set Segment Size.
2. Enter the number of blocks in the window that opens, and click the OK button.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Prefetch multiplier

1. Select the menu option LUN ® Prefetch ® Set Prefetch Multiplier.
2. Enter the multiplier number in the window that opens, and click the OK button.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Segment multiplier

1. Select the menu option LUN ® Prefetch ® Set Segment Multiplier.
2. Enter the multiplier number in the window that opens, and click the OK button.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

Maximum prefetch

1. Select the menu option LUN ® Prefetch ® Set Maximum Prefetch.
2. Enter the number of blocks in the window that opens, and click the OK button.

A confirmation window opens.

3. In the confirmation window, click the Yes button.

To use the Change Prefetch Parameters window to change prefetch parameters

1. Display the Array Configuration window (see "To display the Array Configuration window").
2. In the LUN selection area of the Array Configuration window, select the LUN whose parameters you want to change.
3. Select the menu option LUN ® Prefetch ® Change Prefetch Parameters.

The Change Prefetch Parameters window for the selected LUN opens, similar to the following sample.

Figure 7-3. Sample Change Prefetch Parameters window for a RAID 5 LUN





4. If you want to change the general prefetch parameters



1. To change the prefetch type, click the button for the type you want.

For example,



Prefetching works best when the host issues many large sequential read requests to a physical unit. The SP monitors I/O for sequential reads and, if it finds that any occur, prefetches data automatically.

If the amount of data to be read varies from request to request, you should specify variable prefetch type (the default). If the amount of data read is fairly constant for each request, you should specify constant prefetch type.

2. To change the type of data retention, click the Favor Prefetch button if you want the SP to retain prefetched data over requested data in the read cache, and click the Equal Priority button if you want the SP to treat both types of data equally.

For example,



You should specify Favor Prefetch for most applications. If the server's operating system does not provide software caching, you should specify Equal Priority.

3. To change the disable size, in the Disable Size field, enter the number of blocks that determine when the data should not be prefetched for a read request.

For example,



We recommend that you use one of the following sizes: 129 (the default), 257, 513, 1025, 2049. A prefetch operation is not performed for a read request if the amount of data requested is equal to or greater than the disable size.

4. To change the idle count, enter the new count in the Idle Count field.

For example,



You can specify a count of 0 to 100. We recommend that you specify a count of 40 (the default) or higher.



5. If you want to change the constant prefetch parameters



1. To change the prefetch size, enter in the Prefetch Size field the number of blocks that you want prefetched during a single read operation from the LUN.

For example,



You can specify a prefetch size 0 to 2048 blocks.

2. To change the segment size, enter in the Segment Size field the number of blocks that you want retrieved for each read request.

For example,



You can specify a segment size of 0 that is equal to or less than the prefetch size.



6. If you want to change the variable prefetch parameters



1. To change the prefetch multiplier, enter in the Prefetch Multiplier field the multiplication factor that determines the amount of data you want prefetched for each read request.

For example,



You can specify a prefetch multiplication factor of 0 to 32. The amount of data prefetched for each read request equals the number of blocks of data requested multiplied by the prefetch multiplication factor.

2. To change the segment multiplier, enter in the Segment Multiplier field the multiplication factor that determines the amount of data you want retrieved during a single prefetch read operation from the LUN.

For example,



You can specify a segment multiplication factor that is equal to or less than the prefetch multiplier. The amount of data retrieved during a single read operation (segment size) equals the number of blocks of data requested multiplied by the segment multiplication factor. If you specify a segment multiplication factor that is equal to the prefetch multiplier, prefetch operations are not divided into segments. The amount of data prefetched for each read request equals the number of blocks of data requested multiplied by the prefetch multiplier.

3. To change the maximum prefetch size, enter in the Maximum Prefetch field the maximum number of blocks to be prefetched for a read request.

For example,



You can specify 0 to 2048 blocks.



7. Click the OK button to change the prefetch parameters to the values you specified.

A confirmation window opens.

8. In the confirmation window, click the Yes button.

NOTE: The LUN cannot use read caching with the prefetch parameters you specified until you enable the read cache for the SP that owns it (see "Changing any LUN parameter except for the default SP and prefetch parameters").

Transferring default ownership of a LUN from one SP to another

You can transfer default ownership of a LUN from the default SP for the LUN (the primary route to the LUN) to the other SP (the secondary route to the LUN). The default SP is the SP that assumes ownership of the LUN after array power is turned off and then on again. Note that transferring default ownership of a LUN is one way of transferring control of a LUN.

You should use the procedure in this section when one of the following occurs:

• The system operator or service person installed a second SP and you want to assign some of the LUNs to the new SP.
• You want to balance LUNs between two SPs.

Depending on the type of server, you may want to use the procedure if any of the following failure situations occurs:

• A failed SP has been replaced, and you want to transfer control to the working SP.
• The array is connected to two host bus adapters; one adapter or the connection to one adapter fails, and you want the working adapter to access the LUNs owned by the failed adapter.
• When one server in a dual-server configuration fails, and you want the working server to access the failed server's LUNs.

NOTE: The auto assignment parameter for the LUN and the optional Application-Transparent Failover (ATF) software also transfer control of a LUN from one SP to another. For information on the auto assignment parameter, see "Auto assignment state"; for information on ATF, see the Dell OpenManage™ ATF Installation and Operation Guide (P/N 2967C). If you have ATF software on the server, you probably want to use it to handle the failure situations listed above, instead of the procedure described in this section.

Transferring default SP ownership of a LUN from one SP to the other can affect how the operating system accesses the LUN. However, any change you make in ownership does not take effect until the array is powered down and up again.

You transfer default ownership of a LUN using an option on the LUN menu in the Array Configuration window. The LUN menu contains an option for changing SP ownership or for displaying the Change Bind parameters window, which lets you change SP ownership and other bind parameters. This section describes how to change ownership using either method.

To use the LUN menu option to transfer default ownership of a LUN

1. Display the Array Configuration window (see "To display the Array Configuration window").
2. In the LUN selection area of the Array Configuration window, select the LUNs whose default SP you want to change.
3. Select the menu option LUN ® Change Default SP.
4. In the list that appears, select the SP that you want to control the LUN.
5. In the Confirmation window that opens, click the Yes button.
6. Have the system operator or service person power the array down and then up again for the change to take effect.
7. On the servers connected to the array, reboot Windows NT.

To use the Change Bind Parameters window to transfer default ownership of a LUN

1. Display the Array Configuration window for the array with the LUN whose default SP you want to change (see "To display the Array Configuration window").
2. In the LUN selection area of the Array Configuration window, select the LUN whose default SP you want to change.
3. Select the menu option LUN ® Change Bind Parameters.

The Change Bind Parameters window for the LUN opens.

4. In Default SP box, click the button for the LUN without the dot in its button.

For example,



5. Click the OK button.
6. In the Confirmation window that opens, click the Yes button.
7. Have the system operator or service person power the array down and then up again for the change to take effect.
8. On each server connected to the array, reboot Windows NT.

Unbinding a LUN

Typically, you unbind a LUN only if you want to do any of the following:

• Add disk modules to it
• Use its disk modules in a different LUN
• Change the capacity of its disk modules

In any of these situations, you should make sure that the LUN contains the disks modules that you want.

To determine which disk modules make up a LUN

1. Display the Array Configuration window (see "To display the Array Configuration window").
2. In the LUN selection area of the Array Configuration window, select the LUN whose disk modules you want to identify.

In the Disk Field, each disk module comprising the LUN is surrounded by a box with the same color as the box surrounding the selected LUN.

You can also determine which disk modules comprise a LUN using the LUN IDs. If the LUN IDs do not appear in any disk modules in the Disk Field, select this menu option on the Array Configuration window: View ® Show LUN IDs.

To unbind LUNs

CAUTION: Unbinding a LUN destroys any data on it. Before unbinding any LUN, make a backup copy of any data on the unit that you want to retain. Do not unbind the last LUN unless it is absolutely necessary. If you do unbind it, you will have to edit the Data Agent configuration file on the servers connected to the SPs that you will use to bind LUNs. For information on editing this file, see "Editing or checking device information in the Data Agent configuration file".

1. Display the Array Configuration window ("To display the Array Configuration window").
2. In the LUN selection area of the Array Configuration window, select the LUNs you want to unbind.
3. Either click the Unbind LUN button on the LUN toolbar or select the menu option LUN ® Unbind.

A window opens warning you that unbinding causes data loss and asking you to confirm the unbind operation.



4. In the window, click the Yes button to confirm the operation.

A window opens telling you that the LUNs were unbound. The LUN icons disappear from the LUN selection area of the Array Configuration window.

Changing the LUN RAID Type or the number or capacity of a LUN's disk modules

If you want to change the LUN RAID Type or the number or capacity of its disk modules, you must change the bound configuration of a LUN, which means, in effect, that you destroy the LUN and recreate it.

When you want to change the number of disk modules, use the same guidelines as for a new configuration (see "Binding disk modules into LUNs").

NOTE: The disk modules that you use for a LUN must have the same capacity to fully use the modules' disk space.

Changing a LUN RAID type or its number of disk modules

1. Update any worksheets that define your configuration.
2. Back up any information on the LUN that you want to save because unbinding a LUN destroys all information on the LUN.
3. On each server connected to the array, stop all processes on the partitions associated with the LUN on the server, and delete the partitions.
4. Unbind the LUN (see "Unbinding a LUN").
5. If you need any new disk modules for the new configuration, install them as described in the Dell PowerVault™ 650F Rackmount Storage System Installation and Service Guide (P/N 5867C) or the Dell PowerVault™ 651F Deskside Storage System Installation and Service Guide (P/N 3867C).
6. If you want to move a disk module to another slot, remove it and install it in the new slot as described in the Dell PowerVault™ 650F Rackmount Storage System Installation and Service Guide (P/N 5867C) or the Dell PowerVault™ 651F Deskside Storage System Installation and Service Guide (P/N 3867C).
7. Bind the disk modules into the desired LUNs (see "Bind parameters").
8. Make the newly created LUNs available to Windows NT.

Upgrading an array with higher capacity modules

You can replace any disk modules in an array with higher capacity modules, as long as you do not replace all disk modules that contain the LIC database at the same time. These disk modules are the ones with disk IDs 00, 01, and 02.

If you want to replace all the disk modules in an array, use the procedure that follows.

CAUTION: Do not power off the array during the following procedure.

To replace all the disk modules in an array

1. Unbind the LUNs whose disk modules you want to replace (see "Unbinding a LUN").
2. Replace all the disk modules you want to replace except for the disk module in 00.
3. Download LIC to the array.
4. Replace the 00 disk module.
5. Bind the disk modules into the desired LUNs (see "Bind parameters").

When you bind the LUNs, the SP copies the LIC to the 00 disk module from the other database disk modules.

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