Creating arrays and logical drives – Dell PERC 4/DC User Manual
Page 30
The drive displays as HOTSP.
5.
Save the configuration.
Objects Menu
1.
On the Management Menu select Objects—> Physical Drive.
A physical drive selection screen appears.
2.
Select a hard drive in the READY state and press <Enter> to display the action menu for the drive.
3.
Press the arrow keys to select Make HotSpare and press <Enter>.
The selected drive displays as HOTSP.
Creating Arrays and Logical Drives
for the configuration procedures.
After you create an array or arrays, you can select the parameters for the logical drive.
contains descriptions of the parameters.
Table 5-1. Logical Drive Parameters and Descriptions
Parameter Description
RAID Level The number of physical drives in a specific array determines the RAID levels that can be implemented with the array.
Stripe Size Stripe Size specifies the size of the segments written to each drive in a RAID 1, 5, or 10 logical drive. You can set the stripe size to 8 KB, 16
KB, 32 KB, 64 KB, or 128 KB. The default is 64 KB.
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, select a small stripe size.
Write
Policy
Write Policy 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. This setting is recommended in standard mode.
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.
Write-through caching has a data security advantage over write-back caching. Write-back caching has a performance advantage over write-
through caching.
NOTICE:
If WriteBack is enabled and the system is quickly turned off and on, the RAID controller may hang when flushing cache memory.
Controllers that contain a battery backup will default to WriteBack caching.
NOTE:
You should not use write-back for any logical drive that is to be used as a Novell NetWare volume.
NOTE:
Enabling clustering turns off write cache. PERC 4/DC and PERC 4e/DC support clustering.
Read
Policy
Read-ahead enables the read-ahead feature for the logical drive. You can set this parameter to Read-Ahead, No-Read-ahead, or Adaptive.
The default is Adaptive.
Read-ahead specifies that the controller uses read-ahead for the current logical drive. Read-ahead capability allows the adapter to read
sequentially ahead of requested data and store the additional data in cache memory, anticipating that the data will be needed soon. Read-
ahead supplies sequential data faster, but is not as effective when accessing random data.
No-Read-Ahead specifies that the controller does not use 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 No-Read-Ahead; however, all requests are still evaluated for possible sequential operation.
Cache
Policy
Cache Policy applies to reads on a specific logical drive. It does not affect the Read-ahead cache. The default is Direct I/O.
Cached I/O specifies that all reads are buffered in cache memory.