Creating arrays and logical drives, Using easy configuration – Dell PERC 4/DC User Manual
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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
Using Easy Configuration
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 2 KB, 4
KB, 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.
NOTE:
Using a 2 KB or 4 KB stripe size is not recommended.
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 supports 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 and writes 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 and writes are buffered in cache memory.
Direct I/O specifies that reads and writes 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.
Span
The choices are:
Yes—Array spanning is enabled for the current logical drive. The logical drive can occupy space in more than one array.
No—Array spanning is disabled for the current logical drive. The logical drive can occupy space in only one array.
The RAID controller supports spanning of RAID 1 and 5 arrays. You can span two or more RAID 1 arrays into a RAID 10 array and two or
more RAID 5 arrays into a RAID 50 array.
For two arrays to be spanned, they must have the same stripe width (they must contain the same number of physical drives).