Chapter 1. Introduction
10
iSCSI
The iSCSI standard, as ratified by the Internet Engineering Task Force (IETF) in
February 2003, provides a guideline for supporting the various capabilities of the iSCSI
protocol. There are features that are specified by the governing organization to be
mandatory and other features that can be optional. Spectra Logic supports all required
features of the iSCSI specification for target devices.
Note:
The required features for iSCSI could be changed by the iSCSI
governing organization.
NDMP
NDMP is an option that can be purchased and enabled for the i1000 (see the NDMP
product directory at
www.ndmp.org/products/index.shtml
applications and NAS devices). The i1000 supports Version 2 and Version 3 of NDMP
(see
www.ndmp.org
for more information about NDMP protocol versions).
Sharing Tape Devices
Both iSCSI and NDMP allow a set of tape resources to be shared between multiple
hosts.
Caution:
Care must be taken to ensure that multiple requests are not
being sent to the same tape drive at the same time.
With NDMP, there is typically a backup application server that manages access to the
tape drives. Even though multiple NAS devices can access the tape device, these
requests are routed through a single backup server that is responsible for managing
access to the drives. As long as the devices and NAS clients are configured properly in
the software, resource contention is eliminated. Access to NDMP functionality is also
password protected—any host wishing to utilize the NAStape must authenticate
themselves with the correct username and password (set up in the backup software).
With iSCSI, there may be many backup applications on many hosts, all responsible for
managing their own access to the tape drives, and as the NAStape looks like a locally
attached resource to each configured host, each host has no idea that other hosts also
have access.
There are several ways to manage resource contention with iSCSI. First, the NAStape
drive will only be visible to hosts where the individual devices are installed. Next,
devices that are shared among multiple servers can be locked during use by a backup
