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Andy,

Thanks a lot for the advice!
I'll try the "olb.shed" option.
Perfect spread is not really required - approximate equipartition of 
datasets is good enough.

Is it possible to add a "rebalance" tool to the xrootd set of utilities?

When I extended existing farm with brand new nodes, my new datasets are 
all directed to new machines, since disks there are empty.
As I understand "opt.sched" will solve the problem for new datasets.
Great.

But it would be nice to redistribute/rebalance the old datasets over the 
whole extended farm.

I guess, for pure xrootd configuration it doesn't really matter that 
much, but I'm working with PROOF farm.
And for PROOF local data placement is important.

This would be a great addition to Xrootd and a big help for admins of 
PROOF clusters.

Cheers,
	Sergey


Andrew Hanushevsky wrote:
> Hi Sergey,
> 
> Actually, youy shouldn't need to do anything, really; if you've set up a 
> default cluster, the redirector will automatically try to load balance 
> using a round-robbin algorithm, this presumes that each server has "enough"
> space. If either assumption is not the case, then read on...
> 
> The particular configuration options you need to consider are:
> 
> olb.sched
> olb.space
> 
> If you haven't specified sched then selection will be on a round-robbin 
> basis. Exactly what you want. So, check for that.
> 
> Make sure that space allows servers to be selected. All the redirector 
> wants to know is that a server has enough space (i.e., more than the 
> disk minimum that can be specified with the space directive). The 
> default is 10GB.
> 
> When copying files, make sure to copy them in set order. That way, they 
> will be spread out across all your servers. Note, however, copying in 
> new files will not be instantaneous since the redirector tries to 
> confirm that no other copy exists. Therefore, copy them in parallel to 
> amortize the wait cost across the copies. I am in the process is 
> simplifying this by creating a commandline "prepare" program that will 
> allow you to prime the redirector for the incomming files and 
> practically avoid the waits altogether.
> 
> In any case, don't expect a perfect spread. Timing issues always creep 
> in and make the selection process not 100% deterministic. This usually 
> annoys perfectionsists but, in practice, works just as well.
> 
> Andy
> 
> On Fri, 22 Feb 2008, Sergey Panitkin wrote:
> 
>> Hi experts,
>>
>> I would like to copy a set of files to an xrootd farm, so that each 
>> farm node gets an equal number of files from that set, regardless of 
>> what the file sizes are and regardless of available/used disk space on 
>> each node.
>>
>> Is there an easy way to accomplish this using xrdcp ?
>>
>> Cheers,
>>     Sergey
>>