On Tue, Feb 16, 2010 at 04:47:11PM -0800, Christo Kutrovsky wrote: > One of the ideas that sparkled is have a "max devices" property for > each data set, and limit how many mirrored devices a given data set > can be spread on. I mean if you don't need the performance, you can > limit (minimize) the device, should your capacity allow this.
There have been some good responses, around better ways to do damage control. I thought I'd respond separately, with a different use case for essentially the same facility. If your suggestion were to be implemented, it would be in the form of a different allocation policy, when selecting vdevs and metaslabs for writes. There is scope for several alternate policies addressing different requirements, in future development, and some nice XXX comments about "cool stuff could go here" accordingly. One of these is for power-saving, with MAID-style pools, whereby the majority of disks (vdevs) in a pool would be idle and spun down, most of the time. This requires expressing very similar kinds of preferences, for what data goes where (and when). AIX's LVM (not the nasty linux knock-off) had similar layout preferences, for different purposes - you could mark lv's with allocation prefernces to the centre of spindles for performance, or other options, and then relayout the data accordingly. I say "had", it presumably still does, but I haven't touched it in 15 years or more. -- Dan.
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