On Dec 21, 2013 12:32 PM, "shacky" <shacky83@xxxxxxxxx> wrote:
>>
>> I all depends on the replication level you use, but let's assume 3.
>
>
> Does replication level 3 mean that the data are all replicated three times in the cluster?
>
Replication is set on a per pool basis. You can set some, or all, pools to replica size of 2 instead of 3.
>> So you get the capacity of one machine.
>>
>> 4 * 1000 * 1000 / 1024 /1024 = 3.81TB
>>
>> This would result in 15.24TB of raw space per machine, so 45TB of raw capacity in the cluster.
>>
>> You probably shouldn't fill the disks over 80% just to be safe. So with 3x replication you have 12.2TB of usable storage.
>
>
> From 45TB to 12.2TB? So less?
> I would expect something similar to RAID5 (about 36GB of usable storage).
> I think I don't understand how Ceph works: could you help me to understand well?
>
Ceph uses replication not erasure coding (unlike RAID). So data is completely duplicated in multiple copies. Erasure coding is scheduled for the Firefly release, according to the roadmap.
-JJ Galvez
>
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