With a k+m which is 3+2 each RADOS object is broken into 5 shards. By default the pool will have a min_size of k+1 (4 in this case). Which means you can lose 1 shard and still be >= min_size. If one host goes down and you use a host-based failure domain (default) you will lose 1 shard out of all PGs on that host. You will now be at min_size and so still readable/writeable. If you lose another host you will now be below min_size with 3 healthy shards for some subset of PG (those common to the 2 hosts) will be inactive and therefore not read/writeable. As you can see, the higher your M the more disks/hosts you can lose before dropping below min_size. Respectfully, *Wes Dillingham* wes@wesdillingham.com LinkedIn <http://www.linkedin.com/in/wesleydillingham> On Mon, Nov 27, 2023 at 1:36 PM <tranphong079@gmail.com> wrote:

Hi Groups,

Recently I was setting up a ceph cluster with 10 nodes 144 osd, and I use S3 for it with pool erasure code EC3+2 on it.

I have a question, how many osd nodes can fail with erasure code 3+2 with cluster working normal (read, write)? and can i choose better erasure code ec7+3, 8+2 etc..?

With the erasure code algorithm, it only ensures no data loss, but does not guarantee that the cluster operates normally and does not block IO when osd nodes down. Is that right?

Thanks to the community. _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io