You may had some mis-understanding on crush choose algo. see crush_do_rule https://github.com/ceph/ceph/blob/master/src/crush/mapper.c#L900 In a simple statement, 1-7 are basic crush rule DSL. 8-13 are tuning parameter for some particular step. a minimal crush rule consists of 1. take, telling which crush bucket to start with 2. choose/chooseleaf, the repeated choose procedure 3. emit, output selected result the default replication rule looks like: take root // from the root bucket chooseleaf firstn 0 host // recursive to leaf of root, ensuring each selective bucket will not conflict on host level emit // as it words a more complex rule like, take one from bucket datecenter-1 and others from datacenter-2 bucket: take datecenter-1 chooseleaf firstn 1 host emit take datacenter-2 chooseleaf firstn -1 host emit -EOF On Tue, Jun 16, 2020 at 6:58 PM Bobby <italienisch1987@gmail.com> wrote:

Hi all,

I have a question regarding following rules in Ceph CRUSH map:

enum crush_opcodes { /*! do nothing */ CRUSH_RULE_NOOP = 0, CRUSH_RULE_TAKE = 1, /* arg1 = value to start with */ CRUSH_RULE_CHOOSE_FIRSTN = 2, /* arg1 = num items to pick */ /* arg2 = type */ CRUSH_RULE_CHOOSE_INDEP = 3, /* same */ CRUSH_RULE_EMIT = 4, /* no args */ CRUSH_RULE_CHOOSELEAF_FIRSTN = 6, CRUSH_RULE_CHOOSELEAF_INDEP = 7,

CRUSH_RULE_SET_CHOOSE_TRIES = 8, /* override choose_total_tries */ CRUSH_RULE_SET_CHOOSELEAF_TRIES = 9, /* override chooseleaf_descend_once */ CRUSH_RULE_SET_CHOOSE_LOCAL_TRIES = 10, CRUSH_RULE_SET_CHOOSE_LOCAL_FALLBACK_TRIES = 11, CRUSH_RULE_SET_CHOOSELEAF_VARY_R = 12, CRUSH_RULE_SET_CHOOSELEAF_STABLE = 13 };

Can we skip specific rules ? Or lets say, what are the minimum number of rules required by CRUSH?

Because my understanding is, it all depends on map hierarchy. If we have a particular/given hierarchy, we can skip certain rules? _______________________________________________ Dev mailing list -- dev@ceph.io To unsubscribe send an email to dev-leave@ceph.io