The previous email had mistakes in the rack a2 and a3 bucket
definition. I missed the a2-2 and a3-2 hosts. It should be:
rack a2 {
id -8
alg straw
hash 0
item a2-1 weight 3.0
item a2-2 weight 3.0
}
rack a3 {
id -9
alg straw
hash 0
item a3-1 weight 3.0
item a3-2 weight 3.0
}
Sorry about that!
>On Sat, Aug 18, 2018 at 9:43 PM Cody <[email protected]> wrote:
>
> Hi everyone,
>
> I am new to Ceph and trying to test out my understanding on the CRUSH
> map. Attached is a hypothetical cluster diagram with 3 racks. On each
> rack, the first host runs 3 SSD-based OSDs and the second 3 HDD-based.
>
> My goal is to create two rules that separate SSD and HDD performance
> domains (by using device class) and both rules should use a*rack*
> level failure domain.
>
> Here is my CRUSH map:
>
> # Devices
>
> device 0 osd.0 class ssd
> device 1 osd.1 class ssd
> device 2 osd.2 class ssd
> device 3 osd.3 class hdd
> device 4 osd.4 class hdd
> device 5 osd.5 class hdd
> device 6 osd.6 class ssd
> device 7 osd.7 class ssd
> device 8 osd.8 class ssd
> device 9 osd.9 class hdd
> device 10 osd.10 class hdd
> device 11 osd.11 class hdd
> device 12 osd.12 class ssd
> device 13 osd.13 class ssd
> device 14 osd.14 class ssd
> device 15 osd.15 class hdd
> device 16 osd.17 class hdd
> device 17 osd.17 class hdd
>
> # Buckets
>
> host a1-1 {
> id -1
> alg straw
> hash 0
> item osd.0 weight 1.00
> item osd.1 weight 1.00
> item osd.2 weight 1.00
> }
>
> host a1-2 {
> id -2
> alg straw
> hash 0
> item osd.3 weight 1.00
> item osd.4 weight 1.00
> item osd.5 weight 1.00
> }
>
> host a2-1 {
> id -3
> alg straw
> hash 0
> item osd.6 weight 1.00
> item osd.7 weight 1.00
> item osd.8 weight 1.00
> }
>
> host a2-2 {
> id -4
> alg straw
> hash 0
> item osd.9 weight 1.00
> item osd.10 weight 1.00
> item osd.11 weight 1.00
> }
>
> host a3-1 {
> id -5
> alg straw
> hash 0
> item osd.12 weight 1.00
> item osd.13 weight 1.00
> item osd.14 weight 1.00
> }
>
> host a3-2 {
> id -6
> alg straw
> hash 0
> item osd.15 weight 1.00
> item osd.16 weight 1.00
> item osd.17 weight 1.00
> }
>
> rack a1 {
> id -7
> alg straw
> hash 0
> item a1-1 weight 3.0
> item a1-2 weight 3.0
> }
>
> rack a2 {
> id -8
> alg straw
> hash 0
> item a2-1 weight 3.0
> }
>
> rack a3 {
> id -9
> alg straw
> hash 0
> item a3-1 weight 3.0
> }
>
> row a {
> id -10
> alg straw
> hash 0
> item a1 6.0
> item a2 6.0
> item a3 6.0
> }
>
> # Rules
>
> rule ssd {
> id 1
> type replicated
> min_size 2
> max_size 11
> step take a class ssd
> step chooseleaf firstn 0 type row
> step emit
> }
>
> rule hdd {
> id 2
> type replicated
> min_size 2
> max_size 11
> step take a class ssd
> step chooseleaf firstn 0 type row
> step emit
> }
>
>
> Q1: Is the above CRUSH map correct for my goal?
>
> Q2: What does the "step choose" and "step chooseleaf" mean? I read its
> definitions in the documentation several times, but still cannot get
> it.
>
> Any helps would be greatly appreciated!
>
> Regards,
> Cody
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