Overland Storage SnapServer Administrator's Manual page 117

SnapServer 7.0 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
page 6-22
iSCSI Multi-Initiator Support
The Support Multi-Initiator checkbox allows two or more initiators to simultaneously access a
single iSCSI target. Multi-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: GuardianOS 7.0 supports Windows 2003 and Windows 2008 Server failover clustering.
When the checkbox for Support Multi-Initiator is selected, a warning message
(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.) appears. 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 caches 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.
10400317-001 10/2011
for more information).
GuardianOS volumes on a Traditional RAID configuration, see
page 5-14.
©2010-11 Overland Storage, Inc.
6 – Other Storage Options
"Configuring VSS/VDS for iSCSI Disks" on
"Volume Properties" on
6-18