Feature #4305: CRUSH: it should be possible use ssd as primary and hdd for replicas but still make sure no replica is on same host - RADOS - Ceph

Actions

Copy link

Feature #4305

open

CRUSH: it should be possible use ssd as primary and hdd for replicas but still make sure no replica is on same host

Added by Corin Langosch about 11 years ago. Updated about 6 years ago.

Status:

New

Priority:

Normal

Assignee:

Category:

Target version:

% Done:

Source:

Community (user)

Tags:

Backport:

Reviewed:

Affected Versions:

Component(RADOS):

CRUSH

Pull request ID:

Description

http://ceph.com/docs/master/rados/operations/crush-map/

rule platter {
ruleset 3
type replicated
min_size 0
max_size 10
step take platter
step chooseleaf 0 type host
step emit
}

rule ssd {
ruleset 4
type replicated
min_size 0
max_size 10
step take ssd
step chooseleaf 0 type host
step emit
}

rule ssd-primary {
ruleset 4
type replicated
min_size 0
max_size 10
step take ssd
step chooseleaf 1 type host
step emit
step take platter
step chooseleaf -1 type host
step emit
}

Using this example it could happen that the primary and one replica end up on the same host if a host contains both ssd and hdd drives. It should be possible to write crush rules which ensure that the data will always be spread over n-replicas hosts, even when a host has sdd and hdd drives.

Actions

Copy link

Updated by Corin Langosch about 11 years ago

Here's an idea how it could work:

rule ssd-primary {
ruleset 4
type replicated
min_size 0
max_size 10
step take ssd
step chooseleaf 1 type host
step pick
step take platter
step chooseleaf 0 type host
step pick
step emit unique
}

Actions

Copy link

Updated by Patrick Donnelly about 6 years ago

Project changed from Ceph to 15
Subject changed from it should be possible use ssd as primary and hdd for replicas but still make sure no replica is on same host to CRUSH: it should be possible use ssd as primary and hdd for replicas but still make sure no replica is on same host