Ok, so I've misunderstood the meaning of failure domain. If there is no
way to request using 2 osd/node and node as failure domain, with 5 nodes
k=3+m=1 is not secure enough and I will have to use k=2+m=2, so like a
raid1 setup. A little bit better than replication in the point of view
of global storage capacity.
Patrick
Le 05/12/2023 à 12:19, David C. a écrit :
Hi,
To return to my comparison with SANs, on a SAN you have spare disks to
repair a failed disk.
On Ceph, you therefore need at least one more host (k+m+1).
If we take into consideration the formalities/delivery times of a new
server, k+m+2 is not luxury (Depending on the growth of your volume).
________________________________________________________
Cordialement,
*David CASIER*
________________________________________________________
Le mar. 5 déc. 2023 à 11:17, Patrick Begou
<Patrick.Begou@xxxxxxxxxxxxxxxxxxxxxx> a écrit :
Hi Robert,
Le 05/12/2023 à 10:05, Robert Sander a écrit :
> On 12/5/23 10:01, duluxoz wrote:
>> Thanks David, I knew I had something wrong :-)
>>
>> Just for my own edification: Why is k=2, m=1 not recommended for
>> production? Considered to "fragile", or something else?
>
> It is the same as a replicated pool with size=2. Only one host
can go
> down. After that you risk to lose data.
>
> Erasure coding is possible with a cluster size of 10 nodes or more.
> With smaller clusters you have to go with replicated pools.
>
Could you explain why 10 nodes are required for EC ?
On my side, I'm working on building my first (small) Ceph cluster
using
E.C. and I was thinking about 5 nodes and k=4 m=2. With a failure
domain
on host and several osd by nodes, in my mind this setup may run
degraded
with 3 nodes using 2 distincts osd by node and the ultimate
possibility
to loose an additional node without loosing data. Of course with
sufficient free storage available.
Am I totally wrong in my first ceph approach ?
Patrick
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