Dell H310 User Manual

Contents

Dell H310 User Manual Manual pdf 18 page image

Virtual Disk Read Cache PoliciesThe read policy of a virtual disk determines how the controller handles reads to that virtual disk. The read policies are:• Always Read Ahead—Allows the controller to read sequentially ahead of requested data and to store theadditional data in cache memory, anticipating that the data is required soon. This speeds up reads for sequentialdata, but there is little improvement when accessing random data.• No Read Ahead—Disables the Read-Ahead capability.• Adaptive Read Ahead—Begins using Read-Ahead if the two most recent disk accesses occurred in sequentialsectors. If the read requests are random, the controller reverts to No Read Ahead mode.NOTE: The default read cache setting for virtual disks is Adaptive Read Ahead.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 reconfiguration operation iscomplete.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 can beexpanded within that free space.• If a virtual disk is created and it does not use the maximum size of the disk group, free space is available.Free space is also available when a disk group’s physical disks are replaced by larger disks using the Replace Memberfeature. A virtual disk's capacity can also be expanded by performing an OCE operation to add more physical disks.RAID Level Migration (RLM) refers to changing a virtual disk’s RAID level. Both RLM and OCE can be done at the sametime so that a virtual disk can simultaneously have its RAID level changed and its capacity increased. When a RLM/OCEoperation is complete, a reboot is not required. See the following table for a list of RLM/OCE possibilities. The sourceRAID level column indicates the virtual disk RAID level before the RLM/OCE and the target RAID level column indicatesthe RAID level after the operation has completed.NOTE: If the controller already contains the maximum number of virtual disks, you cannot perform a RAID levelmigration or capacity expansion on any virtual disk.NOTE: The controller changes the write cache policy of all virtual disks undergoing a RLM/OCE to Write-Throughuntil the RLM/OCE is complete.Table 3. RAID Level MigrationSource RAIDLevelTarget RAID Level Number ofPhysical Disks(Beginning)Number ofPhysical Disks(End)CapacityExpansionPossibleDescriptionRAID 0 RAID 0 1 2 or more Yes Increasescapacity byadding disksRAID 0 RAID 1 1 2 No Converts non-redundant virtual18