HP StoreOnce Backup - Manual (Page 136)

14 Hard disk replacement
In this chapter:
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RAID
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How do I know a disk has failed?
•
Replacing a hot-plug hard disk
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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.
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HP D2D4312 and HPD2D4324 Backup Systems
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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.
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18 TB for the HP D2D4324 Backup System and 18 TB for each of up to three Capacity
Upgrade Kits
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9 TB for the HP D2D4312 Backup System and 9 TB for each of up to three Capacity Upgrade
Kits
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9 TB for the HP D2D4112 Backup System and 9 TB for an attached Capacity Upgrade Kit
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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.
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HP D2D2504 Backup Systems
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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:
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1.5 TB for the HP D2D2502i Backup System
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3.0 TB for the HP D2D2504i Backup System
136 Hard disk replacement