CRUSH

[Fyodor Ustinov <ufm@ufm.su>]

Hi!

Two questions.

1-st. As I understand it - any usable changes of CRUSH map on active 
cluster can't destruct data? In the worst case (for example, I managed 
to put two osd in one rack, and now I have two copies of the data in a 
single rack) I get information about the degradation and this will be 
fixed automatically?

2-nd. How to correct edit crush map in case "rack"?

Let's say I have such a map:

device 0 device0
device 1 device1
device 2 device2
device 3 device3
device 4 device4

# types
type 0 device
type 1 host
type 2 rack
type 3 root

# buckets
host host0 {
         id -1
         alg straw
         hash 0  # rjenkins1
         item device0 weight 1.000
}
...
host host4 {
         id -5
         alg straw
         hash 0  # rjenkins1
         item device4 weight 1.000
}
rack rack0 {
         id -6
         alg straw
         hash 0  # rjenkins1
         item host0 weight 1.000
}
...
rack rack4 {
         id -10          # do not change unnecessarily
         alg straw
         hash 0  # rjenkins1
         item host4 weight 1.000
}
root root {
         id -11          # do not change unnecessarily
         alg straw
         hash 0  # rjenkins1
         item rack0 weight 1.000
         item rack1 weight 1.000
         item rack2 weight 1.000
         item rack3 weight 1.000
         item rack4 weight 1.000
}

# rules
rule data {
         ruleset 1
         type replicated
         min_size 2
         max_size 2
         step take root
         step chooseleaf firstn 0 type host
         step emit
}

And now i want add one "rack" and add one "osd" to this rack. How should 
I deal with "id"?

WBR,
     Fyodor.