Question & Answer
Question
Why does DUPTAP or DUPMEDBRM take longer than my backup?
Answer
Some reasons for degraded DUPTAP/DUPMEDBRM performance are:
Note: Since DUPMEDBRM uses DUPTAP 'under the covers', all references to DUPTAP include DUPMEDBRM.
DUPTAP in many cases is not going to be as fast as the save. There are many variables as to why,
here are several:
Note: Since DUPMEDBRM uses DUPTAP 'under the covers', all references to DUPTAP include DUPMEDBRM.
DUPTAP in many cases is not going to be as fast as the save. There are many variables as to why,
here are several:
- Using software encryption,
- Duplicating data with small block sizes
- Inadequate CPU. In most typical configurations a DUPTAP should use less than 10% of the CPU
- DUPTAP is sensitive to memory pool size.
- Check HW configuration for bottlenecks, such as two ultra high speed tape drives on an IO adapter that cannot allow both tape drives to run at full speed, tape and DASD sharing a bus, etc.
- The DUPTAP command does not do fast positioning like the SAVxxx commands so it takes longer to position the tape to the proper sequence. If the input or output tapes are not beginning at sequence 1 there could be significant time spent positioning the tape(s). DUPTAP and DUPMEDBRM will use fast positioning beginning with IBM i 7.4 PTF SI74085, which is also included in IBM i 7.4 TR PTF Group level 3, IBM i 7.3 PTF SI74084, which is also included in IBM i 7.3 TR PTF Group level 9, or IBM i 7.2 PTF SI74083 (See 'Improved Performance for Duplicating Tape Media - IBM i 7.4 and 7.3 and 7.2' below)
- Verify that ALL IOPless/NPIV/Virtualization PTFs are installed. See the appropriate section in the 'IBM Removable Media on IBM i' located at: http://tinyurl.com/IBMi-Removable-Media
- For a save there is only one tape to position, but for a dupe there are two. If both the input and output tapes need to be positioned to some other sequence than sequence #1 the seek time is greater for the dupe. This is magnified because DUPTAP does not do 'fast positioning' unless the DUPTAP/DUPMEDBRM performance enhancement provided by IBM i 7.4 PTF SI74085, which is also included in IBM i 7.4 TR PTF Group level 3, IBM i 7.3 PTF SI74084, which is also included in IBM i 7.3 TR PTF Group level 9, or IBM i 7.2 PTF SI74083 are applied (See 'Improved Performance for Duplicating Tape Media - IBM i 7.4 and 7.3 and 7.2' below).
- It also depends on rewind, unload, mounts, etc. Finally, the label processing by BRMS. All those things double for a dupe verses save.
- For a save, once we get down to the actual data, we are going from multiple DASD arms to one tape device. For a dupe, we are solely using the tape devices.
- For a dupe, we are throttled by both tape devices because we can't write something we haven't read, and we can't let the input device get too far ahead of the output device. So if the input device has to wait at all, even for a small amount of time, the output device has to wait. If the output device has to wait, and there are no more buffers for the input devices to use, then the input device has to wait on the output device. For a save, in general, if a system has enough DASD and memory resources, the save can keep up with the tape drive so we get optimal performance.
- The difference is data dependent. In cases where a large number of small objects or a lot of spooled files are being saved, the dupe may go faster than the save. If large database objects are being saved the tape drive is going to be kept busy, so a dupe of that data will generally end up being slower because the I/O rates for a dupe are slower than the I/O rates for a save.
Improved Performance for Duplicating Tape Media - IBM i 7.4 and 7.3 and 7.2
IBM i 7.4 TR 3 and IBM i 7.3 TR 9 and IBM i 7.2 provides a performance improvement when copying the contents of one tape to another using the Duplicate Tape (DUPTAP) or Duplicate Media using BRM (DUPMEDBRM) commands. If a file to be duplicated is not at the beginning of the media, these commands will now directly position the tape to the file instead of searching for it by reading every file label on the media. This may also help reduce media wear by limiting the number of full media passes needed to position the tape. Note that performance is improved only when the starting files are not at the beginning of the media.
Software Requirements
IBM i 7.4 PTF SI74085, which is also included in IBM i 7.4 TR PTF Group level 3
IBM i 7.3 PTF SI74084, which is also included in IBM i 7.3 TR PTF Group level 9
IBM i 7.2 PTF SI74083
Note: Load/Dump tasks are not involved in DUPTAP
[{"Product":{"code":"SWG60","label":"IBM i"},"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Component":"Operating System","Platform":[{"code":"","label":"iSeries"},{"code":"PF012","label":"IBM i"}],"Version":"Version Independent","Edition":"Enterprise","Line of Business":{"code":"LOB57","label":"Power"}}]
Was this topic helpful?
Document Information
Modified date:
06 October 2020
UID
nas8N1000040