load balancing question

[John E. Malmberg]

Richard Sharpe wrote:
> On Tue, 8 Oct 2002, René Nieuwenhuizen wrote:
> 
>>Richard Sharpe wrote:
>>
>>
>>>On Mon, 7 Oct 2002, John E. Malmberg wrote:
>>>
>>>>Javid Abdul-AJAVID1 wrote:
>>>>   
>>>>>MSDFS is filey system right, how will it help to load balance samba
>>>>>connections
>>>>>     
>>>>MSDFS does not really load balance.  MSDFS distributes the 
>>>>subdirectories of a directory between multiple servers transparently to 
>>>>the clients.
>>>>   
>>Wouldn't it be easy to run a script on the msdfs-root that monitors the 
>>load on different machines and that recreates the referrals based on 
>>this load.
> 
> Sure, but it seems better to defer the re-ordering of the referrals until 
> someone asks :-) That's what we plan to do, and then try to do policy 
> based stuff, like if this machine has more capacity currently, hand out it 
> at the top of the list, and order them by power as well, like P4s before 
> PIIIs etc.

In order for that to work the underlying cluster file system must 
support simultaneous access from the multiple hosts.

If you have that, then you do not need to deal with the MSDFS feature.

If you do not have that, then you can not load balance between servers, 
unless you completely replicate all of the data.  And that will only 
help if all the access is read only.


There are only a limited number of Operating Systems / File Systems that 
support simultaneous shared access from multiple hosts, like OpenVMS 
clusters do.  And I am not aware of any of them that will support the 
number of hosts or the distance that OpenVMS does.

Most of the systems on UNIX use a primary / secondary relationship where 
only one host is ever directly accessing the filesystems, and the other 
hosts are using a network type interconnection to access the files.

These primary / secondary systems are good for fail-over cases, but not 
load balancing.  Any file access from a secondary is much slower and 
resource intensive than access from the primary.  Also switching the 
file serving from the primary to a secondary is not a cost free operation.

So redirectly clients to a secondary server usually will mean that the 
data must travel on the wire twice, unless the secondary server has a 
good caching mechanism.


So it all comes down to what the underlying platform supports for shared 
simultaneous disk access.

Or finding out the exact requirements for the project to see what all 
the options are.

-John
wb8tyw at qsl.network
Personal Opinion Only