HP LTO 4 FC, LTO 4 SCSI manual Factors affecting performance, Ways of optimizing performance, page

4 Factors affecting performance

This chapter contains techniques and information to help you design software applications so that they use the tape drive’s potential as efficiently as possible.

•Ways of optimizing performance:

	•	Ensuring the recommended minimum transfer sizes	page 27
	•	Identifying the media type page 28
	•	Using Cartridge Memory instead of tape headers	page 28
	•	Using the Performance Log page to diagnose problems page 28
•	Time-out values to help you tune timings in backup applications page 28
•	Log pages—recommended support page 29
•	Factors affecting performance, relating separately to the host, drive and format page 29

Ways of optimizing performance

HP’s Ultrium drives are high-performance products. Application software may require significant enhancement in order to capitalize on this speed. There are a number of areas to look at and these are discussed below.

Further details can also be found in the “How to optimize the performance of hp ultrium tape drives” white paper.

Detecting the drive’s speed

Applications should not key off Inquiry strings in order to tell the difference between different speed drives. It is better to use the Performance Log page see under the LOG SENSE command in Chapter 4, “Commands”, of SCSI Interface, Volume 3 of the HP LTO Ultrium Technical Reference Manual.

In the Performance Log page (34h), parameter 04h (Native data rate) gives the native data rate of the drive in units of 100 KB/s. LTO 4 drives give the value 04B0h, indicating 120 MB/s with Ultrium 4 media or no cartridge loaded. If a previous generation cartridge is loaded, the value will be lower.

Ensuring the recommended minimum transfer sizes

Use the Data Compression Log page. HP cannot diagnose performance issues without accurate reporting of the current compression or the average compressibility over a backup session. Make sure that you report the log page.

Regarding HP’s One-Button Disaster Recovery (OBDR) feature (see “One-Button Disaster Recovery (OBDR)” on page 89), it is important to note that in some situations the SCSI block size may have to be fixed for a given tape for format reasons. This means that if the host writes 2 KB blocks to support OBDR, it may have to continue to write 2 KB blocks for the rest of the tape; it depends on the format compatibility required by the overall system. However as HP Ultrium drives are insensitive to

HP LTO Ultrium 4 drives technical reference manual, volume 2: software integration 27 HP restricted