First off: what does weight actually mean in a CRUSH map? I had
assumed it was there to balance capacity, and should be set to
something proportional to the size of the disk. However, the page on
the wiki about osd_auto_weight seems to indicate that it's related to
disk performance, not size. Is it one of these, or something
completely different?
Also: when defining several levels of buckets, how does the weight on
the higher levels of buckets affect the overall distribution? I've got
the beginning of a cluster running now, with one host with a 640GB
drive and a 1TB drive, and another host with a 640GB drive. I've been
playing with the weights to try and get the amount of data on each
disk proportional to its size, to maximize the space I have available.
I have my CRUSH map set up like this right now:
host0 {
item device 0 weight 0.640
item device 1 weight 1.000
}
host1 {
item device 2 weight 0.640
}
root {
item host0 weight 1.640
item host1 weight 0.640
}
Will this do what I'm expecting, and maximize the amount of data I can
store before any of the disks fill up?
Thanks,
--Ravi
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