Adaptec 5325301507 - Snap Server 4400 NAS, Administrator'S Manual

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RAIDs
52 SnapServer Administrator Guide
drives as a hot spare. The following table summarizes the advantages and
disadvantages of each type of RAID.
Caution
To reduce exposure to double-drive disk failures on RAID 5, use no more
than eight drives in a single RAID set and group smaller RAID sets together.
Local and Global Hot Spares
A hot spare is a disk drive that can automatically replace a damaged drive in a
RAID 1, 5, 6, or 10. Designating a disk drive as a hot spare helps ensure that data is
available at all times. If one disk drive in a RAID fails or is not operating properly,
the RAID automatically uses the hot spare to rebuild itself without administrator
intervention. SnapServers offer two kinds of hot spares: local and global.
Features RAID 0 RAID 1 RAID 5 RAID 6 RAID 10
Data Loss Risk Highest Lowest Low Lower Very Low
Write Access Speeds Fastest Fast Medium Slower Faster
Usable Capacity Highest Lowest High Medium Low
Disks Required 1 or more 2 or more 3 or more 4 or more 4 or more
Supports Hot Spares No Yes Yes Yes Yes
Item Description
Definitions Local (hot) spare — A local (or dedicated) hot spare is associated
with and is available only to a single RAID. Administrators typically
create a local hot spare for RAIDs containing mission-critical data that
must always be available.
Global (hot) spare — A hot spare that may be used for any RAID 1, 5,
6, or 10 in the system (assuming sufficient capacity) as necessary.