Reclamation Vs Move Data

[LarryB]

Hi all,

Like most people I find reclamation a slow and clumsy process. It seems to take longer than expected. How does it work? Like it appears to read back to the server, then to the target tape. Does not go to disk!!! The movement of files is very slow.

Is it better to write script to implement move data? Is it more efficent? My understanding is to use reconstruct=yes to maintain file aggregates. What is this?

regards
Laurence

 

[javajockey]

You did not mention if you were talking about onsite or offsite reclamation.
To answer your question, "Scripting" the task of manual reclamation will probably provide you with zero benefit. To understand why the task is slow, you have to understand how data is written to tape. If you are reclaiming a tape that is 10% full, Your tape drive will spend most of it's time "fast forwarding" through the "white space", to get to the actual data portion of the tape. If data is scattered all across the tape, reclamation will take even longer. Performing a "move data" will probably not make this task any faster since most of the delay is mechanical. The reclamation job will always "target" the volume with the most "reclaimable" "full" tape. To get a better idea of how this process works, there is an excellent explanation in the TSM redbook.

 

[BBB]

The only advantage to scripting it with move data is you get to choose which volumes to reclaim rather than tsm choosing for you. Move data recons=yes is identical to reclamation of the same volume, there will be no difference in time ... except for offsite reclamation ...

Reclamation of offsite volumes is different, the order chosen is not based on their %util, there are other calculations instead. Another key difference is offsite reclamation will reclaim all volumes that meet your threshold simultaneously to reduce the number of onsite tape mounts performed. So if you've got 100 volumes offsite that are all reclaimable according to your reclaim threshold - it will reclaim them all at the same time. Usually this means it just never ever ever finishes doing any of them So you can use the offsitereclaimlimit=X parameter to change this, for example set it to 5 and it will only ever try to reclaim at most 5 volumes at a time. At least this way it might finish some of them each day. Personally I think the best setting for this is about the number of tapes you have time to reclaim in 1-2 days.

 

[javajockey]

I have found that running reclamation while I'm allowing clients to backup seems to work best. Otherwise, my drives are sitting idle.

 

[LarryB]

Thanks for your reply. There are many Redbooks for TSM, can you remember (or close ot it) the title of the Redbooks.

 

[javajockey]

http://www.redbooks.ibm.com/abstracts/sg244877.html

P 242

 

[sps]

@BBB
doubt???
"Reclamation of offsite volumes is different, the order chosen is not based on their %util, there are other calculations instead"
can u explain me........

 

[BBB]

Do a offsite reclamation (you might want to set offsitereclaimlimit=4 or something to limit it) and watch the volumes the reclamation process picks for reclamation, and their order in the activity log. Then check those volumes properties with q vol f=d. You will see they are not selected or ordered by %util. When I looked a year or so ago the tapes selected correlated with the last_read_date but occasionally one sneaks in that doesn't fit - can't explain that.