Local And Global Spares - Overland Storage SnapServer Administrator's Manual

SnapServer/GuardianOS 7.5 Administrator's Guide
The following table summarizes the advantages and disadvantages of each type of RAID.
Features
Data Loss Risk
Write Access Speeds
Usable Capacity
Disks Required
Supports Spares
CAUTION:
drives in a single RAID set and group smaller RAID sets together. RAID 6 is recommended for
RAID sets with more than four drives.

Local and Global Spares

A spare is a disk drive that can automatically replace a failed drive in a RAID 1, 5, 6, or 10 set.
Designating a disk drive as a 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 spare to
rebuild itself without administrator intervention. SnapServers offer two kinds of spares: local
and global.
10400541-001
RAID 0
Highest
Fastest
Highest
1 or more
No
To reduce exposure to double-drive disk failures on RAID 5, use no more than eight
Item Description
Definitions Local (hot) spare – A local (or dedicated) spare is associated with and
is available only to a single RAID. Administrators typically create a local
spare for RAIDs containing mission-critical data that must always be
available.
Global (hot) spare – A spare that may be used for any RAID 1, 5, 6, or
10 in the system on any unit (assuming sufficient capacity) as it
becomes needed.
Identifying Spares are identified on the Storage > Disks page using the
following icons:
Each icon will be associated with a disk in the RAID, identifying that
disk as either a local spare or a global spare.
Interaction When a drive in a RAID fails, the system looks for a spare in the
following order:
1. If a local spare dedicated to the RAID exists, use the local spare.
2. If no local spare is available, and there is a single global spare of
sufficient capacity, use the global spare.
3. If no local spare is available, and two global spares of different
capacity are available, use the smaller global spare with sufficient
capacity.
©2008-14 Overland Storage, Inc.
RAID 1 RAID 5
Lowest Low
Fast Medium
Lowest High
2 or more 3 or more
Yes Yes
5 - Traditional RAID Storage
RAID 6 RAID 10
Lower Very Low
Slower Faster
Medium Low
4 or more 4 or more
Yes Yes
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