Hi Ravi,
On Sun, 2010-11-07 at 23:52 -0800, Ravi Pinjala wrote:
> 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?
It is the size of the disk, for example:
osd1, size 120GB, weight: 1.200
osd2, size 560GB, weight: 5.600
osd3, size 340GB, weight: 3.400
Now, you should be careful, since osd2 and osd3 will have to do much
more IOps, so make sure their hardware is up to the job.
>
> 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?
You don't have to calculate a hosts weight in the root, this will be
done automatically by summing the device's weight.
But, it looks fine what you've done, that should work.
Wido
>
> Thanks,
> --Ravi
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