[Lustre-discuss] Redundancy with object storage?

[Brian J. Murrell]

On Tue, 2007-12-04 at 17:59 -0600, D. Dante Lorenso wrote:
> 
> What happens when you try to read a file from the OST that is down?

That depends on whether the OST has been configured for failout or
failover.  In failover mode, the assumption is that another node will
resume service for that OST, so I/O to objects on the failed OST will
block, waiting for the service to be resumed.  In failout mode, I/O to
the failed OST will return EIOs.

> I'm 
> guessing that read will hang for a considerable period of time.

For ever, or until the OST is repaired in the case of failover, yes.

> Likely 
> that hanging will eventually occur for many files on a box

On a given client, yes.
 
> simultaneously and the whole box will lock up waiting on I/O it will 
> never get

No.  Having even a lot of processes blocked on I/O to a failed OST will
not "lock up" a whole client.  The client will continue to run and
complete tasks that are not dependent on the failed OST.

>  ... essentially taking the whole shebang down.

I guess it depends on how you define shebang.

> Is the road map posted somewhere?

First (non-ad-sponsored) hit on google for "lustre roadmap":
http://www.clusterfs.com/roadmap.html

>   URL?  Any timeline I might want to 
> watch and wait for?

Server Network Striping.  Looks like 2.0 in Q4 2008.

> Right, like RAID 1, but at the network level.

Which is what drbd is effectively.

> I have configured a DRBD system with heartbeat in my lab tests and it 
> seems to work well enough, but I haven't tied it into Lustre just yet.

Adding Lustre should not be a big hurdle.
 
> It is a delicate mounting/unmounting game to ensure that partitions are 
> monitored, mounted, and fail-over in just the right order.

Indeed.

> I'm leaning toward doing the L,D,H solution, but was really hoping for 
> something easier.  Are there any online howtos that demonstrate that 
> configuration?

I don't know of any HOWTO/cookbook to it.  If you implement it, perhaps
you could create the HOWTO.  :-)

b.