Asus SCSI 320-0 Global Array Manager Transition Tool - Page 79

Action, Stripe size, Write policy, Read-ahead, Cache policy, KB, 8 KB, 16 KB, 32 KB, 64 KB

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Using Easy Configuration, Continued Step Action 6 Set the stripe size, cache write policy, Read policy, and I/O (cache) policy from the Advanced Menu. Stripe size This parameter specifies the size of the segments 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. The default stripe size is 64 MB. A larger stripe size provides better read performance, especially if your computer does mostly sequential reads. However, if you are sure that your computer does random read requests more often, choose a small stripe size. Write policy This parameter specifies the cache write policy. You can set the write policy to Write-back or Write-through. The default is 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. If WriteBack is enabled and the system is quickly turned off and then on, MegaRAID may hang when flushing cache memory. Adapters that contain a battery backup will default to WriteBack caching. Adapters which contain a battery will default to WriteBack. 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 that is 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. The default setting is Normal. Normal specifies that the controller does not use read-ahead for the current logical drive. 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. The default setting is Direct I/O. Cached I/O specifies that all reads are buffered in cache memory. Direct I/O specifies that reads are not buffered in cache memory. 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. Cont'd Chapter 4 MegaRAID Manager 71

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Chapter 4 MegaRAID Manager
71
Using Easy Configuration,
Continued
Step
Action
6
Set the stripe size, cache write policy, Read policy, and I/O (cache) policy from the
Advanced Menu.
Stripe size
This parameter specifies the size of the segments 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. The default stripe size is 64 MB.
A larger stripe size provides better read performance, especially if your computer does
mostly sequential reads. However, if you are sure that your computer does random read
requests more often, choose a small stripe size.
Write policy
This parameter specifies the cache write policy. You can set the write
policy to
Write-back
or
Write-through
. The default is
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.
If WriteBack is
enabled and the system is quickly turned off and then on, MegaRAID may hang when
flushing cache memory. Adapters that contain a battery backup will default to WriteBack
caching. Adapters which contain a battery will default to WriteBack.
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 that is 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.
The default
setting is
Normal.
Normal
specifies that the controller does not use read-ahead for the current logical drive.
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. The default setting is
Direct I/O
.
Cached I/O
specifies that all reads are buffered in cache memory.
Direct I/O
specifies that reads are not buffered in cache memory. 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.
Cont’d