Parity Management - Overland Storage SnapServer Administrator's Manual

SnapServer 7.0 Administrator's Guide

Parity Management

Parity is set either when creating a new storage pool, or when modifying an existing storage
pool to either increase parity by adding a new drive, or decrease parity to expand storage
space (and sacrifice redundancy). Parity and snapshot space are selected by the user
according to the best estimate of necessary storage requirements.
A move from dual parity to single parity is allowed at any time, provided the storage pool is
healthy. A move from single parity to dual parity is only allowed when a new disk drive is
added that is large enough to support the new parity mode.
NOTE: A storage pool that was converted from dual parity to single parity cannot be converted
To Add a Disk Drive to Upgrade Parity
To increase the parity protection, new disk drives can be added to empty slots in the
SnapServer. The DynamicRAID will then obtain user input on how you want to use the
new, additional space.
If no disk drives can be added, a warning is issued that the changes cannot be made without
deleting the storage pool or resetting the environment back to factory defaults.
When a new disk drive is added, the Administration Home page displays the message
Disks Detected
detected (click to use)
shown. You can then change the parity and snapshot settings for the storage pool to take
advantage of the additional space.
NOTE: Disk drives that have been previously configured can be added; they are indicated in the
There are no separate spare or global spare disk drives when using the DynamicRAID
option. With single parity, if a disk drive fails, a warning is issued and the system reverts to
a degraded mode with no protection, so that a second drive failure will cause the system to
1
This includes a drive that has any kind of storage configuration on it (from any machine, including the
current one) that is not recognized by the server. For example, the drive was added; the drive was removed;
the drive was in the server and added to a RAID; or the RAID was deleted. In addition, this note applies to
drives that are current RAID members and may have been removed (possibly inadvertently); upon re-
insertion, they will not be automatically incorporated, regardless of whether automatic incorporation of
unassigned drives is turned on.
10400317-001 10/2011
back to dual parity until a new disk drive is added. This is due to the extra dual-parity
drive that was rolled into the single-parity RAID set.
No. of Disks Impact of Adding One More Disk
1 Parity is upgraded from no parity to single parity.
2 Dual parity option is activated:
• If dual parity selected, system migrates to it.
• If single parity kept, filesystem space is
3 The filesystem space is expanded and, if dual parity
has been selected to replace single parity,
migration commences.
. Going to the Storage > Storage Pools page displays a message,
. When you click the link, the Storage Pool Properties
list by the icon and a message stating that the disk has previously been used in a
different system.
©2010-11 Overland Storage, Inc.
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