HP DDS/DAT tape drives UNIX, Linux and OpenVMS configuration guide (DW049-90930, May 2010)

Using large block sizes

A block size no larger than 256 KB (262144 bytes) is strongly recommended when working with

HP-UX and tape or VTL devices. Backup applications should be configured to work with I/O block

sizes that are no larger than 256 KB. Please check your application documentation to find out how

to check or configure block sizes used for transfers to and from tape or VTL devices.

This is because, by default, the HP-UX stape driver processes a block size larger than 256 KB by

subdividing it into 256 KB blocks for writing to tape (giving a net effect of 256 KB I/O transfers)

For example a 1 MB block (1048576 bytes) is written to tape as four 256 KB blocks. During restore,

stape attempts to reconstruct the original block size that was larger than 256 KB with the 256 KB

blocks from tape. This subdivision and subsequent reconstruction process of block sizes larger than

256 KB adds unnecessary complexity and risk to tape positioning and restore operations and offers

no net gain in terms of increased block size. It should therefore be avoided.

Configuring an autoloader

1. Reboot the system with the autoloader attached.

2. Run ioscan -funC autoch to find the device files for the autoloader.

If there are no device files listed, proceed as follows:

3. Create /dev/rac if it does not exist.

4. Run ioscan -funC tape to find the tape device file.

5. Execute: ls -al /dev/rmt/<device_file>

This will return an output similar to:

2 bin bin 205 0x0450c0

This example tells you that the card number is 4 and the target number 5.

6. Run mknod to create the device files:

mknod /dev/rac/c<X>t<Y>d<Z> c 203 0x0<X><Y><Z>00

where:

<X> is the card number

<Y> is the target number

<Z> is the LUN

For example, using values from the ls -al output above and a LUN of 1, you would execute:

mknod /dev/rac/c4t5d1 c 203 0x045100

To verify that the autoloader has installed correctly, run the following mc command:

mc -p /dev/rac/<device_file> -rIDSM

This will display the various elements in the autoloader.

This will display the various elements in the autoloader. For more details of the mc command,

run man mc.

The maximum block size limit of 256 KB (262144 bytes) applies to all versions of HP-UX and is strongly recommended for

broad backup/restore compatibility across all supported HP-UX versions. Different HP-UX kernel configurations or later versions

of HP-UX may not use 256 KB ‘chunks’ as described; however all HP-UX versions and kernel configurations are compatible

and interoperable with a block size limit of 256 KB.

HP (HP-UX) servers and workstations14