Asus SCSI 320-0 Global Array Manager Transition Tool - Page 36

Cached I/O, Direct I/O

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Using View/Add Configuration, Continued Step Action 8 Set the logical drive size. Move the cursor to Size and press . By default, the logical drive size is set to all available space in the array(s) being associated with the current logical drive, accounting for the Span setting and for partially used array space. For example, if the previous logical drive used only a part of the space in an array, the current logical drive size is set to the remaining space by default. 9 Open the Advanced menu to set the remaining options. Stripe size This parameter specifies the size of the segment written to each disk in a RAID 1, 3, 5, 10, 30 or 50 logical drive. You can set the stripe size to 2 KB, 4 KB, 8 KB, 16 KB, 32 KB, 64 KB, or 128 KB. A larger stripe size produces higher read performance, especially if your computer does mostly sequential reads. However, if your computer does random read requests more often, choose a smaller stripe size. The default is 64 MB. Write Policy This parameter specifies the cache write policy. You can set the write policy to write-back or write-through. In Write-back caching, the controller sends a data transfer completion signal to the host when the controller cache has received all the data in a transaction. In Write-through caching, the controller sends a data transfer completion signal to the host when the disk subsystem has received all the data in a transaction. This is the default setting. Write-through caching has a data security advantage over write-back caching, whereas write-back caching has a performance advantage over write-through caching. You should not use write-back for any logical drive to be used as a Novell NetWare volume. Read-ahead This parameter enables the SCSI read-ahead feature for the logical drive. You can set this parameter to Normal, Read-ahead, or Adaptive. Normal specifies that the controller does not use read-ahead for the current logical drive. This is the default setting. Read-ahead specifies that the controller uses read-ahead for the current logical drive. Adaptive specifies that the controller begins using read-ahead if the two most recent disk accesses occurred in sequential sectors. If all read requests are random, the algorithm reverts to Normal, however, all requests are still evaluated for possible sequential operation. Cache Policy This parameter applies to reads on a specific logical drive. It does not affect the Read ahead cache. Cached I/O specifies that all reads are buffered in cache memory. Direct I/O specifies that reads are not buffered in cache memory. This is the default setting. Direct I/O does not override the cache policy settings. Data is transferred to cache and the host concurrently. If the same data block is read again, it comes from cache memory. Press to exit the Advanced Menu. 10 After you define the current logical drive, choose Accept and press . If space remains in the arrays, the next logical drive to be configured appears. Repeat steps 6 to 9 to configure another logical drive. If all array space is used, a list of the existing logical drives appears. Press any key to continue. Respond to the Save prompt. 11 Initialize the logical drives you have just configured. See Initializing Logical Drives on page 29. 28 MegaRAID Configuration Software Guide

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MegaRAID Configuration Software Guide
28
Using View/Add Configuration,
Continued
Step
Action
8
Set the logical drive size. Move the cursor to
Size
and press <Enter>. By default, the
logical drive size is set to all available space in the array(s) being associated with the
current logical drive, accounting for the
Span
setting and for partially used array space.
For example, if the previous logical drive used only a part of the space in an array, the
current logical drive size is set to the remaining space by default.
9
Open the Advanced menu to set the remaining options.
Stripe size
This parameter specifies the size of the segment written to each disk in a
RAID 1, 3, 5, 10, 30 or 50 logical drive. You can set the stripe size to 2 KB, 4
KB, 8 KB, 16 KB, 32 KB, 64 KB, or 128 KB. A larger stripe size produces
higher read performance, especially if your computer does mostly sequential
reads. However, if your computer does random read requests more often,
choose a smaller stripe size. The default is 64 MB.
Write Policy
This parameter specifies the cache write policy. You can set the write
policy to write-back or write-through.
In
Write-back
caching, the controller sends a data transfer completion signal to the host
when the controller cache has received all the data in a transaction.
In
Write-through
caching, the controller sends a data transfer completion signal to the
host when the disk subsystem has received all the data in a transaction. This is the default
setting.
Write-through caching has a data security advantage over write-back caching, whereas
write-back caching has a performance advantage over write-through caching.
You should
not use write-back for any logical drive to be used as a Novell NetWare volume.
Read-ahead
This parameter enables the SCSI read-ahead feature for the logical drive.
You can set this parameter to
Normal, Read-ahead
, or
Adaptive.
Normal
specifies that the controller does not use read-ahead for the current logical drive.
This is the default setting.
Read-ahead
specifies that the controller uses read-ahead for the current logical drive.
Adaptive
specifies that the controller begins using read-ahead if the two most recent disk
accesses occurred in sequential sectors. If all read requests are random, the algorithm
reverts to Normal, however, all requests are still evaluated for possible sequential
operation.
Cache Policy
This parameter applies to reads on a specific logical drive. It does not
affect the Read ahead cache.
Cached I/O
specifies that all reads are buffered in cache memory.
Direct I/O
specifies that reads are not buffered in cache memory. This is the default
setting.
Direct I/O does not override the cache policy settings. Data is transferred to cache and
the host concurrently. If the same data block is read again, it comes from cache memory.
Press <Esc> to exit the Advanced Menu.
10
After you define the current logical drive, choose
Accept
and press <Enter>. If space
remains in the arrays, the next logical drive to be configured appears. Repeat steps 6 to 9
to configure another logical drive. If all array space is used, a list of the existing logical
drives appears. Press any key to continue. Respond to the Save prompt.
11
Initialize the logical drives you have just configured. See Initializing Logical Drives on
page 29.