Overland Storage SnapServer Administrator's Manual page 130

SnapServer/GuardianOS 7.5 Administrator's Guide
• Do Not Use the GuardianOS Snapshots Feature on a Volume or Storage Pool
Containing an iSCSI Disk – Running a GuardianOS snapshot on a volume or storage
pool containing an iSCSI disk will abruptly disconnect any clients attempting to write to
the server's iSCSI disk, and the resulting snapshot may contain inconsistent data.
Supported Windows servers can create a native snapshot of a SnapServer iSCSI disk
using VSS (see
information).
iSCSI Multi-Initiator Support
Check the Support Multiple Initiators box to allow two or more initiators to simultaneously
access a single iSCSI target. Multiple initiator support is designed for use with applications or
environments in which clients coordinate with one another to properly write and store data on
the target disk. Data corruption becomes possible when multiple initiators write to the same
disk in an uncontrolled fashion.
NOTE: RAINcloudOS supports Windows 2003 and Windows 2008 Server failover clustering.
When the box for Support Multiple Initiators is checked, a warning message appears:
Uncontrolled simultaneous access of multiple initiators to the same
iSCSI target can result in data corruption. Only enable Multi-
Initiator Support if your environment or application supports it
It functions as a reminder that data corruption is possible if this option is used when creating
an iSCSI disk.
Write Cache Options with iSCSI Disks
NOTE: This section refers only to iSCSI disks. For information about configuring write cache on
To ensure the fastest possible write performance, SnapServers can buffer up to 1GB of data to
efficiently handle data being transmitted to a SnapServer. This widely accepted method of
improving performance is not without some risk. For example, if the SnapServer were to
suddenly lose power, data still in cache would be lost.
This risk can be minimized by following industry-standard security precautions, such as
keeping servers in a secured location and connecting power supplies to the mains using a
network- or USB-based UPS. In most environments, taking these simple precautions virtually
eliminates the risk of serious data loss from sudden and unexpected power outages.
Of course, the physical conditions and company policies that guide IT decisions vary widely.
Power outages are a common occurrence in some areas, and data protection procedures vary
from company to company. Administrators who determine that the risk of data loss, even with
security cautions in place, outweighs the significant increase in write performance that write
cache provides, can disable this feature for individual iSCSI disks.
When working with write cache for iSCSI disks, note the following:
• Write cache can be disabled on an iSCSI-disk-by-iSCSI-disk basis. Disabling write cache
for an iSCSI disk does not disable write cache for any other iSCSI disk or any other
resources on the SnapServer.
• The write cache for an iSCSI disk can be enabled/disabled any time using the Web
Management Interface. However, to change it no active sessions can be connected to the
iSCSI disk.
10400541-001
Configuring VSS/VDS for iSCSI Disks
GuardianOS volumes on a Traditional RAID configuration, see
Chapter 5.
©2008-14 Overland Storage, Inc.
6 - Other Storage Options
on page 125 for more
Volume Properties in
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