Den fre 26 juni 2020 kl 10:32 skrev Zhenshi Zhou <deaderzzs@xxxxxxxxx>: > Hi all, > > I'm going to deploy a cluster with erasure code pool for cold storage. > There are 3 servers for me to set up the cluster, 12 OSDs on each server. > Does that mean the data is secure while 1/3 OSDs of the cluster is down, > or only 2 of the OSDs is down , if I set the ec profile with k=4 and m=2. > By default, crush will want to place each part (of 6 in your case for EC 4+2) on a host of its own, to maximize data safety. Since you can't do that with 3 hosts, you must make sure no more than 2 pieces end up on a single host ever, so you can't just move from failure-domain=host to domain=osd, since that would place all 6 pieces on the same host but different OSDs which would be bad. You need to make the crush rule pick two different OSDs per host, but not more. One way could be to make a tree where hosts has half of its OSDs in one branch and the other half in another (lets call it subhost in this example), then you get 3*2 subhosts, and you make crush pick placement from subhosts and it will always put two pieces per OSD host, never on the same OSD and it will allow one host to be down for a while. I would like to add that data is not very secure when you have no redundancy at all left. Machines will crash, they will require maintenance, patches, bios updates and things like that, and having NO redundancy while you have planned or unplanned downtime will be placing the data at huge risk, _any_ surprise in this situation would immediately lead to data loss. Also, if one box dies, the cluster can't run and can't recover until you have a new host back in, so you are already running at the edge of data safety in your normal case. Even if this will "work", ceph as being a cluster really should have N+1 hosts or more if your data split (replication factor or EC k+m) is equal to N. -- May the most significant bit of your life be positive. _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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