Chapter 4. Overview
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devices. The Spectra 2K library supports Version 2 and Version 3 of NDMP (see
www.ndmp.org for more information about NDMP protocol versions).
Serverless Backup
Serverless Backup is sometimes referred to as Third Party Copy or Extended Copy
(X-copy). Serverless Backup is a backup architecture in which data flows directly from
one storage device to another, bypassing the server. Serverless Backup is made
possible when storage devices support the X-copy commands as specified in the SCSI
protocol. The X-copy command set allows a device to read blocks of data from another
compliant device. In a serverless backup environment, the Spectra Logic library reads
data from the disk device and writes it directly to tape.
This backup process requires a backup application that has X-copy functionality.
Serverless backups are normally performed in Storage Networking environments since
data can be shared by multiple hosts or initiators. The backup application is
responsible for determining which blocks on the disk get backed up to tape.
Sharing Tape Devices
iSCSI and NDMP both 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. This server 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 library must
authenticate themselves with the correct username and password. This is also generally
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 library 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 tape drives
attached to library will only be visible to hosts where the individual devices are
installed. Next, devices that are shared among multiple servers can be locked during
