Use the Logical Drive Properties dialog to specify the modification priority, cache properties, and media scan properties of a selected logical drive. Also, you can view the progress of a logical drive modification operation on this dialog.
How to Access the Logical Drive Properties Dialog
To access the Logical Drive Properties dialog, select a logical drive in the Logical View; then select either (1) the
Logical Drive >> Properties pull-down menu option, or (2) Properties from the right-mouse pop-up menu.
Result: The Logical Drive Properties dialog is displayed.
The Base tab of the Logical Drive Properties dialog displays the following logical drive data: logical drive name, world wide name, status, capacity, RAID level, and segment size.
The modification priority defines how much processing time is allocated for logical drive modification operations relative to system performance. You can increase the logical drive modification priority, although this may affect system performance.
Operations affected by the modification priority include:
The following priority rates are available.
Note: The Lowest priority rate favors system performance, and the modification operation will take longer. The Highest priority rate favors the modification operation, and system performance may suffer.
To set the modification priority, click and hold the settings button on the slider bar and move it to the desired priority.
The progress bar at the bottom of the Logical Drive Properties dialog displays the progress of an operation.
You can view the progress of the following operations:
* The Progress Bar label shows "Modification progress" rather than the operation name.
Important: The storage management software cannot obtain progress information from the controllers in the Storage Subsystem if the network management connection to the controllers is down or if the Storage Subsystem is partially managed. In this case, the progress bar on the dialog displays "zero percent complete" and the text above the progress bar displays "<operation> progress data unavailable." For more information on a partially managed Storage Subsystem or a Unresponsive controller or Storage Subsystem condition, see the Enterprise Management Window help system.
Cache memory is an area of temporary volatile storage (RAM) on the controller that has a faster access time than the actual drive media. By using cache, you can increase overall application performance because:
To measure cache effectiveness, examine the cache hit percentage in the Performance Monitor. This statistic shows the percentage of data requests that are serviced by the cache and did not require a disk access. See Monitoring Performance.
Use the Cache Properties tab to enable or set the following cache parameters.
Note: In certain situations, the controller may temporarily suspend caching operations when caching is not appropriate. This status is called Enabled but Not Active.
Cache Parameter | Description |
Read Caching | Allows read operations from the host to be stored in controller cache memory. If a host requests data that is not in the cache, the controller goes to disk, reads the needed data blocks, and places them in the cache. Until the cache is flushed, all other requests for this data are fulfilled with cache data rather than from a physical disk read, increasing throughput. To enable the read caching parameter, select the Read Caching checkbox. |
Write Caching | Allows write operations from the host to be stored in cache memory. The logical drive data in the cache is written to disk, or flushed, automatically at the interval you specify in the Flush write caching after parameter. Note: There also are cache settings you can set at the Storage Subsystem level that affect all logical drives. Select Storage Subsystem >> Change Cache Settings. For more information, see Specifying Storage Subsystem Cache Settings. To enable the write caching parameter, select the Write Caching checkbox. |
Write cache mirroring |
Allows cached data to be mirrored across redundant controllers with the same cache size. Data written to the cache memory of one controller is also written to the cache memory of the other controller. Therefore, if one controller fails, the other can complete all outstanding write operations. Important: To use this option:
To enable the write cache mirroring parameter, select the Write Cache Mirroring checkbox. Note: This option is available only when write caching is also enabled. |
Write caching without batteries | Allows write caching to continue even if the controller batteries are discharged completely, not fully charged,
or not present. If you select this parameter without a UPS for back-up power, you could lose data if power fails. Enable the Write Caching Without Batteries parameter by selecting the checkbox. Note: This option is only available if write caching is also enabled. |
Cache read-ahead multiplier |
Cache read-ahead allows the controller, while it is reading and copying host-requested data blocks from disk
into the cache, to copy additional data blocks into the cache. This increases the chance that a future request
for data could be fulfilled from the cache. Cache read-ahead is important for multimedia applications that use
sequential I/O. Disabling cache read-aheadIf you need to disable cache read-ahead, select 0 in the cache read-ahead multiplier spinner box. |
A media scan is a background process that runs on all logical drives in the Storage Subsystem for which it has been enabled, providing error detection on the drive media. Enabling the media scan process allows the process to find media errors before they disrupt normal drive reads and writes. The media scan process scans all logical drive data to verify that it can be accessed, and optionally scans the logical drive redundancy data.
Note: You can set the duration over which the media scan runs by selecting the Storage Subsystem >> Media Scan Duration pull-down menu option.
A media scan discovers the following errors and reports them to the Event Log:
Error | Description/Result |
Unrecovered media error | The drive could not read the requested data on its first attempt, or on any subsequent retries. Result: Logical Drives with redundancy protection. Data is reconstructed, rewritten to the drive, and verified. The error is reported to the event log. Logical Drives without redundancy protection (RAID 0 logical drives and degraded RAID 1, 3, and 5 logical drives). The error is not corrected but is reported to the event log. |
Recovered media error | The drive could not read the requested data on its first attempt, but succeeded on a subsequent attempt. Result: The data is rewritten to the drive and verified. The error is reported to the event log. |
Redundancy mismatches | Redundancy errors are found and a media error is forced on the block stripe so that it is found when the drive
is rechecked. If redundancy is repaired, this forced media error is removed. Result: The first 10 redundancy mismatches found on a logical drive are reported to the event log. Note: The media scan checks for redundancy only if the optional redundancy checkbox is enabled. For more information, see Enabling a Redundancy Check, below. |
Unfixable error | The data could not be read, and parity or redundancy information could not be used to regenerate it. For example,
redundancy information cannot be used to reconstruct data on a degraded logical drive. Result: The error is reported to the event log. |
To enable a background media scan for this logical drive, select the Enable background scan check box.
During a redundancy check, all data blocks in a logical drive are scanned, and:
Note: RAID 0 logical drives have no data redundancy.
Select the With redundancy check radio button to enable a redundancy check during a media scan.
To apply all settings of an individual logical drive (modification priority, cache, and media scan) to all other logical drives in the Storage Subsystem, click the Apply Settings to All Logical Drives checkbox. Use this checkbox ONLY if you want all of the logical drives to share the same settings. This option overwrites any current settings on the others logical drives in the Storage Subsystem.