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

SnapServer 7.0 Administrator's Guide
Features
Data Loss Risk
Write Access Speeds
Usable Capacity
Disks Required
Supports Spares
CAUTION:
eight drives in a single RAID set and group smaller RAID sets together. RAID 6 is
recommended for RAIDs with more than four drives.

Local and Global Spares

A 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 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.
Item
Definitions
Identifying
Interaction
10400317-001 10/2011
RAID 0
Highest
Fastest
Highest
1 or more
No
To reduce exposure to double-drive disk failures on RAID 5, use no more than
Description
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 (assuming sufficient capacity) as necessary.
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.
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.
©2010-11 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
5-3