Dell and UCPE-900, UCSE-900, UCSA-901, UCPA-901, UCSB-900, UCPB-900 manual Parameters description

•Stripe element size

•Read policy

•Write policy

•Type of initialization

•Hot spare configuration

NOTE: The default hard drive cache policy for a virtual disk with SAS hard drives is disabled and virtual disk with SATA hard drives is enabled. The Virtual Disk parameter cannot be changed in the BIOS Configuration Utility (<Ctrl> <R>). Use Dell OpenManage Storage Management for the hard drive cache setting operation.

The following table shows the parameters that you can configure when defining virtual disks.

Table 4. Parameters — description

Parameter	Description
RAID Level	Specifies whether the virtual disk is RAID 0, 1, 5, 6, 10, 50, or 60. The number
	of disks, disk capacity, requirements for fault tolerance, performance, and
	capacity should be considered when selecting the RAID level.
Stripe Element Size	Specifies the size of the segments written to each physical disk in a RAID 0, 1,
	5, 6, 10, 50, and 60 virtual disk. You can set the stripe element size to 64 KB
	128 KB, 256 KB, 512 KB, or 1 MB. The default and recommended stripe
	element size is 64 KB.
	A larger stripe element size provides better read performance if your system
	mostly does sequential reads.
Write Policy	Specifies the controller 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.
	NOTE: If a Battery Backup Unit (BBU) is present, the default cache setting
	is Write-Back. If no BBU is present, the default cache policy default
	setting is Write-Through.
	NOTE: If Write-Back is enabled and the system is turned off and then on,
	the controller may pause as the system flushes cache memory.
	Controllers have a battery backup default to Write-Back caching.
	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.
Read Policy	Read-Ahead enables the read-ahead feature for the virtual disk. You can set
	the parameter to Read-Ahead, No-Read-Ahead, or Adaptive-Read-Ahead.
	The default is Adaptive-Read-Ahead.
	Read-Ahead specifies that the controller uses Read-Ahead for the current
	virtual disk. Read-Ahead capability allows the controller to read sequentially
	ahead of requested data and store the additional data in the cache memory,
	anticipating that the data is required soon.

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