On 5/3/2013 4:56 PM, Dimitri Maziuk wrote: > On 05/03/2013 02:53 PM, Josh Fisher wrote: > >> ... What you are >> considering would require a new device assignment each time a new volume >> is needed. While possible, it is way more complex that it appears at >> first glance. > PS. I think the potentially worse can of worms is when you have multiple > devices and some of them are autochangers and some aren't, and while > switching to the next "already mounted" device should be cheaper than > auto-changing the tape in the current device, if the current autochanger > is actually a vchanger over mounted partitions it isn't, and so on and > so forth.
The drives inside of an autochanger are treated like any other device, for the most part. An autochanger resource only groups them together so that assigning an autochanger resource to a storage resource allows the device selection to be limited to ONE of the devices belonging to that autochanger. The autochager isn't assigned to a job at startup, but rather one particular drive (device resource) belonging to that autochanger. That assignment doesn't change for the life of the job. Reassigning a job's device at every media change is possible, it is just more complicated and increases the likelihood of introducing a race condition when more than one job is requesting new media at the same time. There are two different operations happening, device assignment and media assignment. It would be necessary to make selecting both at the same time an atomic operation. So it is just the "normal" complexity of multi-threaded programming, which is always much more complex than it seems. So I think the Bacula devs have just chosen the safety and robustness of keeping it simple, rather than the risk of added flexibility. It's just an engineering choice. ------------------------------------------------------------------------------ Get 100% visibility into Java/.NET code with AppDynamics Lite It's a free troubleshooting tool designed for production Get down to code-level detail for bottlenecks, with <2% overhead. Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap2 _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
