Dell PowerEdge H730P User Manual

Contents

Conditions Under Which Forced Write-Back With No Battery Is EmployedCAUTION: It is recommended that you use a power backup system when forcing Write-Back toensure there is no loss of data if the system suddenly loses power.Write-Back mode is available when you select Force WB with no battery. When Forced Write-Backmode is selected, the virtual disk is in Write-Back mode even if the battery is not present.Virtual Disk Read Cache PoliciesThe read policy of a virtual disk determines how the controller handles reads to that virtual disk. The readpolicies are:Always ReadAheadAllows the controller to read sequentially ahead of requested data and to store theadditional data in cache memory, anticipating that the data is required soon. Thisspeeds up reads for sequential data, but there is little improvement when accessingrandom data.No Read Ahead Disables the Read-Ahead capability.Reconfiguration Of Virtual DisksAn online virtual disk can be reconfigured in ways that expands its capacity and/or change its RAID level.NOTE: Spanned virtual disks such as RAID 10, 50, and 60 cannot be reconfigured.NOTE: Reconfiguring Virtual Disks typically impacts disk performance until the reconfigurationoperation is complete.Online Capacity Expansion (OCE) can be done in two ways:• If there is a single virtual disk in a disk group and free space is available, the virtual disk’s capacity canbe expanded within that free space.• If a virtual disk is created and it does not use the maximum size of the disk group, free space isavailable.Free space is also available when a disk group’s physical disks are replaced by larger disks using theReplace Member feature. A virtual disk's capacity can also be expanded by performing an OCE operationto add more physical disks.RAID Level Migration (RLM) refers to changing a virtual disk’s RAID level. Both RLM and OCE can be doneat the same time so that a virtual disk can simultaneously have its RAID level changed and its capacityincreased. When a RLM/OCE operation is complete, a reboot is not required. The source RAID levelcolumn indicates the virtual disk RAID level before the RLM/OCE operation and the target RAID levelcolumn indicates the RAID level after the RLM/OCE operation.NOTE: If the controller already contains the maximum number of virtual disks, you cannot performa RAID level migration or capacity expansion on any virtual disk.NOTE: The controller changes the write cache policy of all virtual disks undergoing a RLM/OCEoperation to Write-Through until the RLM/OCE operation is complete.21