Dell PowerVault MD3000 Hardware Owner's Manual

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Contents

Dell PowerVault MD3000 Hardware Owner's Manual Manual pdf 34 page image

34 Using Your RAID EnclosureCycle TimeThe media verification operation runs only on selected disk groups, independent of other disk groups.Cycle time is how long it takes to complete verification of the metadata region of the disk group and allvirtual disks in the disk group for which media verification is configured. The next cycle for a disk groupstarts automatically when the current cycle completes. You can set the cycle time for a media verificationoperation between 1 and 30 days. The firmware throttles the media verification I/O accesses to disksbased on the cycle time.The RAID controller module tracks the cycle for each disk group independent of other disk groups onthe controller and creates a checkpoint. If the media verification operation on a disk group is preemptedor blocked by another operation on the disk group, the firmware resumes after the current cycle. If themedia verification process on a disk group is stopped due to a RAID controller module restart, thefirmware resumes the process from the last checkpoint.Virtual Disk Operations LimitThe maximum number of active, concurrent virtual disk processes per controller is four. This limit isapplied to the following virtual disk processes: background initialization, foreground initialization,consistency check, rebuild, and copy back.If a redundant controller fails with existing virtual disk processes, the processes on the failed controllerare transferred to the peer controller. A transferred process is placed in a suspended state if there are fouractive processes on the peer controller. The suspended processes are resumed on the peer controller whenthe number of active processes falls below four.Disk Group OperationsRAID Level MigrationOver time, you may determine that characteristics of the initial RAID level you set initially are no longerappropriate for your enterprise. For example, you can add fault-tolerant characteristics to a stripe set(RAID 0) by converting it to a RAID 5 set. Select the virtual disk that you want to change and select thetype of RAID level to which you want to migrate. MD Storage Manager provides information aboutRAID attributes to assist you in selecting the appropriate level. You can perform a RAID level migrationwhile the system is still running and without rebooting, which maintains data availability.Segment Size MigrationSegment size refers to the amount of data (in kilobytes) that the RAID controller module writes on asingle physical disk in a virtual disk before writing data on the next physical disk. Valid values for thesegment size are 8, 16, 32, 64, 128, 256, and 512 KB.Dynamic segment size migration enables the segment size of a given virtual disk to be changed. Adefault segment size was set when the virtual disk was created, based on such factors as the RAID leveland expected usage. You can change the default value if actual usage does not match your needs.