HP D2D .HP D2D Backup System user guide (EH985-90907, March 2011) - Page 161
Hard disk replacement, RAID - d2d4324 backup system
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14 Hard disk replacement In this chapter: • RAID • How do I know a disk has failed? • Replacing a hot-plug hard disk • After replacing the failed disk RAID RAID 6 RAID 6 provides protection against double disk failures and failures while a single disk is rebuilding. The following HP StoreOnce Backup Systems are RAID 6 devices. • HP D2D4312 and HPD2D4324 Backup Systems • HP D2D4106 and HP D2D4112 Backup Systems The HP StoreOnce Backup System head unit is protected by a RAID 6 volume, and each Capacity Upgrade Kit is protected by a separate RAID 6 volume. Therefore the head and each Capacity Upgrade Kit can experience a double disk failure without incurring a data loss. These HP StoreOnce Backup Systems also have an online spare disk on each shelf, which will automatically be incorporated into the RAID if a disk fails. This means that actual storage capacity is approximately 75% of the physical storage capacity for the main unit and each Capacity Upgrade Kit connected to it. • 18 TB for the HP D2D4324 Backup System and 18 TB for each of up to three Capacity Upgrade Kits • 9 TB for the HP D2D4312 Backup System and 9 TB for each of up to three Capacity Upgrade Kits • 9 TB for the HP D2D4112 Backup System and 9 TB for an attached Capacity Upgrade Kit • 4.5 TB for the HP D2D4106 Backup System and 4.5 TB for an attached Capacity Upgrade Kit RAID 5 The following HP StoreOnce Backup Systems are RAID 5 devices. • HP D2D2504 Backup Systems • HP D2D2502 Backup Systems RAID 5 stores parity data across all the physical drives in the array. If a drive fails, the controller uses the parity data and the data on the remaining drives to reconstruct data from the failed drive. The system continues operating with a slightly reduced performance until you replace the failed drive. RAID 5 requires an array with a minimum of three physical drives. For the HP StoreOnce Backup System, which has four disks, 25% of the total logical drive storage capacity is used for parity data. This means that actual storage capacity is approximately: Backup System user guide 161
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