Using Large Block Sizes; What Next; Selecting A Tape Device To Create Its Device Files (Agile View) - HP EH890–90900 Technical Reference Manual

Figure 5 Selecting a tape device to create its device files (Agile View)
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4. From the right-hand panel on the HP-UX Peripheral Device Tool page, click on Reinstall Device
Files. At the next page, click the Reinstall button. When the browser returns to the HP-UX Peripheral
Device Tool page, click the Refresh button one or more times until the list of device files appears
under the Properties header.

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.

What next?

Once device files have been created, you should confirm that your new tape drive is working properly.
"Verifying the
file to test your installation.
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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.
14 HP (HP-UX) servers and workstations
installation" on page 31 provides instructions on backing up and restoring a sample
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