Best Practices for configuring NetWorker tape devices under
Common Device Interface (CDI) usage:
CDI is a newer industry-wide method of talking to drives compared to old-style magnetic tape input/output. Introduced in 2001 with NetWorker release 7.0 to provide a generic passthrough solution across all operating systems.
- CDI enables the use of the TapeAlert feature.
- CDI enables on-demand autocleaning of tape devices.
- CDI is required for scanning of device serial numbers
- CDI is required for WORM and future encryption support.
Persistent binding and naming:
Enabling persistent binding and naming for tape libraries and tape devices is the recommended best practice to prevent device reordering on reboots or plug and play events. If a device reordering occurs, the NetWorker software is unable to use any affected drives until the configuration is manually corrected.
- Persistent binding is used to ensure that the operating system of a server always sees SAN-presented devices with the same SCSI target ID across reboots.
- Persistent naming is used to ensure that the operating system or device driver of a server always creates and uses the same symbolic path for a device.
Automatic library and device configuration:
The NetWorker software provides the ability to scan, detect, and configure library and tape devices directly from the NetWorker Management Console (NMC) GUI. This is the recommended way to configure libraries, and manual configuration through the jbconfig or jbedit command line tools should be used only in special cases.
Tape drives in virtualized environments:
For any virtualization system that does not provide dedicated HBA capabilities, the use of tape drives in guest containers is not supported for production environments. The reason is that virtualized or passthrough drivers have high interruption rates, are not suitable for sequential input/output, and can cause a high number of SCSI resets, even in the best cases. Support for the use of tape drives in a VMware Virtual Machine (VM) requires specific compatible hardware and VMware versions and must be configured through VMDirectPath.
Device ordering issues arise when an operating system assigns a different device filename for a previously configured device. As a result, tape drives configured in NetWorker no longer match the actual state of the operating system, and NetWorker is no longer able to properly use the tape device. Proper configuration of persistent binding and persistent naming resolves issues regarding device ordering, as the operating system always assigns the same device file regardless of any external events.
Device block sizes:
Block size indicates the size of data on a single transfer to the physical tape. This is dependent on the tape device, SCSI controller, and SCSI controller driver. The NetWorker software has the ability to control block sizes, but only if it is allowed to do so by the operating system. In cases where the operating system assigns a specific value for a block size, NetWorker settings no longer have any impact. It is strongly recommended that the operating system configuration is set to use a variable block size.
For additional information on the above topics and for information on topics like Shoe-shining, Multipathing, SAN best practices, LTO tape drive firmware issues, Hardware-based encryption, LTO Device configuration best practices (OS specific) and Preventing SCSI resets refer to the following document 'Configuring Tape Devices for EMC NetWorker'.