5 The scheduling options

Haizea has several scheduling options that control how Haizea selects resources and schedules leases. For example, the above example assumed that leases can be suspended (which they generally always can be when running as virtual machines). What would happen if this were not possible? You can modify the suspension option in the [scheduling] section to find out:

[scheduling]
...

suspension: none

...

Rerun Haizea. Now, when the AR lease arrives at 13:15, the scheduler will realise it has to preempt the best-effort lease to make room for the AR lease, but will no longer be able to suspend it. The only option is to cancel the best-effort lease and resubmit it to the queue:

[2006-11-25 13:15:00.00] LSCHED  Preempting lease #1...
[2006-11-25 13:15:00.00] LSCHED  ... lease #1 has been cancelled and requeued

Now, the best-effort lease can only be scheduled after the AR lease, at 14:00:

[2006-11-25 13:15:00.00] VMSCHED Lease #1 has been scheduled on nodes [1] 
                                 from 2006-11-25 14:00:00.00 
                                   to 2006-11-25 15:00:00.00

So, the schedule would end up looking like this:

Notice how, although suspending a lease is a disruptive activity which can delay the completion time of a best-effort request, it is still much better than completely cancelling a request and waiting for enough resources to accommodate the entire (uninterrupted) duration of the lease.

Another scheduling option you can modify is whether Haizea should transfer the VM's disk image from an image repository before the lease can start. You can do this by modifying the lease-deployment option:

[general]
...
lease-preparation: imagetransfer
...

If you look at the bottom of the sample configuration file, you will find a section called [deploy-imagetransfer] with all the image transfer options.

Rerun Haizea again. You should get a schedule similar to the previous one, but with some extra messages indicating that image transfers are taking place:

[2006-11-25 13:00:00.00] DEPLOY  Starting image transfer for lease 1
[2006-11-25 13:01:22.00] DEPLOY  Completed image transfer for lease 1

As you can see, the best-effort lease can no longer start right at 13:00, since an image transfer has to take place before the starting time. The same is true of the AR lease, but notice how Haizea schedules the image transfer in such a way that the AR lease can still start at 13:30 as planned (instead of delaying the starting time until 13:31:22).

There are several other options you can modify in the [scheduling] section, such as what backfilling algorithm to use, whether to allow lease migration or not, etc. These options are described in the following chapters, and in Appendix B.