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SnapServer / GuardianOS 7.6 Administrator’s Guide 7 - Other Storage Options
The interaction between the initiator and target mandates a server-client model where the
initiator and the target communicate with each other using the SCSI command and data set
encapsulated over TCP/IP. Overland Storage is one of the first to embed iSCSI target support
in its SnapServers.
Isolate iSCSI Disks from Other Resources for Backup Purposes
It is important to isolate iSCSI disks from other resources on the SnapServer for two reasons:
• The filesystem of an iSCSI disk differs fundamentally from the SnapServer native
filesystem.
• iSCSI disks are managed from client software rather than the SnapServer Web
Management Interface.
For ease of management and particularly for data integrity and backup purposes, either
dedicate the entire SnapServer to iSCSI disks, or if the server is to be used with other shared
resources, place the iSCSI disk and the other shared resources on separate volumes.
• Back up an iSCSI Disk from the Client, not the SnapServer – An iSCSI disk is not
accessible from a share and thus cannot be backed up from the SnapServer. The disk
can, however, be backed up from the client machine from which the iSCSI disk is
managed.
NOTE: While some third-party, agent-based backup packages could technically back up an iSCSI
disk on the SnapServer, the result would be inconsistent or corrupted backup data if any
clients are connected during the operation. Only the client can maintain the filesystem
embedded on the iSCSI disk in the consistent state that is required for data integrity.
• 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 Configuring VSS/VDS for iSCSI Disks on page 153 for more
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.
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
GuardianOS volumes on a Traditional RAID configuration, see Volume Properties in
Chapter 6.
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