PCServer330 - Changing the RAID Parameters

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Service Hints & Tips

Document ID: GSMH-3E8JD7

PCServer330 - Changing the RAID Parameters

Applicable to: World-Wide

Changing the RAID Parameters:
To change the RAID parameters:

1. Start the ServeRAID configuration program (see 'Starting the ServeRAID Configuration Program—).
2. Select Advanced Functions from the Main Menu.
3. Select Change RAID Parameters.

The default settings are:
Stripe unit size - 8K

Attention:
Once the stripe unit is chosen and data is stored in the logical drives, the stripe unit cannot be changed without destroying data in the logical drives.

The stripe unit size is the amount of data written on a given disk before writing on the next disk. To maximize the overall
performance, choose the stripe unit such that the stripe-unit size is close to the size of the system I/O request. The default is set to 8 K data bytes.

Note:
When the stripe unit size is 8 K or 16 K, the maximum number of drives in an array is 16. When the stripe unit size is 32 K or 64 K, the maximum number of drives in an array is 8.

Rebuild Priority --- High:
Rebuild priority can be set to high, medium, or low. When the rebuild request is set to high, the rebuild I/O request gets high priority in the execution order.

When the rebuild request is set to medium in a heavily loaded system (with a medium rate of system I/O requests), the medium-priority rebuild can reduce the disk rebuild time at the expense of degraded handling of I/O requests.

When the rebuild priority is set to low, in a moderate to heavily loaded system, low rebuild priority will increases the disk rebuild time but provides better system performance.

Note:
Rebuild priority can be changed without affecting data in the logical drives.

Unattended Mode --- Off:
You can enable the adapter to accept changes in the configuration without user input. Unattended mode is useful when the server operates remotely. See 'Unattended Mode of Operation— on page 62 for more information.

When Unattended Mode is On, and a hard disk drive is found in a location other than the one defined in the adapter configuration, the program pauses briefly for user input, then, automatically rearranges the configuration information to correct the logical drive configuration. Unattended mode also clears any blocked drives.

When Unattended Mode is Off, the program waits for user input.

Read ahead --- On:
Normally, the RAID adapter transfers data from disk to its local cache in steps of stripe-unit size. This provides excellent overall performance when workloads tend to be sequential. However, if the workload is random and system I/O requests are smaller than stripe-unit size, reading ahead to the end of the stripe unit will result in a wasted SCSI bus bandwidth and wasted disk utilization. When read-ahead is set to Off, the size of data transfer from the disk to local cache is equal to the system I/O request size, and no read-ahead to the end of the stripe unit is performed.

Notes:
1. The read-ahead setting can be changed without destroying data in a logical drive.
2. When the configuration is saved on a diskette, the RAID parameters are saved also.

Unattended Mode of Operation:
You can enable the adapter to accept changes in the configuration without user input. When this mode is enabled (see 'Changing the RAID Parameters— for information), the adapter pauses briefly to permit a user to override the default action; then the adapter rearranges the configuration information. Unattended mode also clears any blocked logical drives. This mode is useful when the server operates remotely.

The adapter 'chooses— an action that is equivalent to pressing one of the following function key:

F5:

The server continues the startup operation after identifying the drive that is defunct. For example, an HSP drive failed to respond during POST. Startup continues without the HSP drive; its drive state will display as DHS.

F6:

When a drive has been removed from the server, for example, for maintenance or security, and was returned, but in a different bay, the adapter adjusts the configuration to the drive's new location.

F7:

An adapter with stored configuration information that does not match that of the configured drives present, imports the configuration information from the drives.

The RAID adapter assigns the following priorities to the function keys:

If this action/key is available

Priority of actions

F7

F7, F6, F5

F6

F6, F5

F5

F5

Search Keywords

Hint Category

Hard Drives, Hardware Maintenance Information

Date Created

12-02-97

Last Updated

22-01-99

Revision Date

28-04-99

Brand

IBM PC Server

Product Family

PC Server 330

Machine Type

8640

Model

TypeModel

Retain Tip (if applicable)

N/A

Reverse Doclinks
and Admin Purposes

F5:	The server continues the startup operation after identifying the drive that is defunct. For example, an HSP drive failed to respond during POST. Startup continues without the HSP drive; its drive state will display as DHS.
F6:	When a drive has been removed from the server, for example, for maintenance or security, and was returned, but in a different bay, the adapter adjusts the configuration to the drive's new location.
F7:	An adapter with stored configuration information that does not match that of the configured drives present, imports the configuration information from the drives.

If this action/key is available	Priority of actions
F7	F7, F6, F5
F6	F6, F5
F5	F5

	Search Keywords
	Hint Category	Hard Drives, Hardware Maintenance Information
	Date Created	12-02-97
	Last Updated	22-01-99
	Revision Date	28-04-99
	Brand	IBM PC Server
	Product Family	PC Server 330
	Machine Type	8640
	Model
	TypeModel
	Retain Tip (if applicable)	N/A
	Reverse Doclinks and Admin Purposes