HP LTO 4 SAS Designing backup applications, Optimizing performance, Large data transfer size

1 Designing backup applications

In today’s computer market, software applications that use tape drives to copy the information from a computer’s hard disk for safe keeping are readily available for many different operating systems. Unfortunately, not all these applications take advantage of the advances made in tape technology over the past few years. This section examines some of the characteristics that a good backup utility should include.

Optimizing performance

There are some fundamental things that tape management applications should implement when dealing with Ultrium drives:

•Use large data transfer sizes.

•Control and monitor data compression.

•Ensure directory information is safe and accurate.

•Maximize the use of the tape drive’s internal buffering capability.

Each of these is discussed below.

For more information on optimizing performance, see “Factors affecting performance” on page 27.

Large data transfer size

Applications should use large data transfer sizes to make better use of the Ultrium drive’s internal buffers. A good goal to set is at least 128 KB each for read or write operation, with an ideal target of 256 KB:

•For fixed-length block mode reads and writes, provided the block size multiplied by the number of blocks to be transferred is at least 128 KB, drives will provide peak performance. Small block sizes (512 bytes) are acceptable so long as they are written and read in fixed-length block mode using large transfers.

•For variable-length block mode reads and writes, the transfer length should be at least 256 KB.

Data compression control

Ultrium drives have built-in hardware data compression. Backup applications should incorporate features to report the actual compression ratio achieved during backup operations.

The typical compression ratio achieved during backup operations on PC and UNIX networks is 2:1, but this can vary widely depending on the actual data being compressed.

For more information, see “Controlling data compression” on page 51.

Non-immediate commands

Performance can be improved by only using immediate mode WRITE FILEMARKS commands.

HP LTO Ultrium 4 drives technical reference manual, volume 2: software integration 11 HP restricted