Hello Felix,

When you put your OS on a single drive and that drive fails, you will loose all the OSDs on that machine, because the entier machine goes down. The PGs that now miss a partner are going to be replicated again. So, in your case, the PGs that are on those 11 OSDs. This rebuilding doesn't start right away, so you can safely reboot an OSD host without starting a major rebalance of your data.

I would put 2 drives in RAID1 if I were you. Putting 2 SSDs in the back 2,5" slots, like suggested by Brian, sounds like the best option to me. This way you don't loose a massive storage amount (2x10x8 = 160 TB you would loose otherwise, just for the OS installation...)

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Kind regards,
Cybertinus

On 12-08-2016 13:41, Félix Barbeira wrote:

Hi,

I'm planning to make a ceph cluster but I have a serious doubt. At this moment we have ~10 servers DELL R730xd with 12x4TB SATA disks. The official ceph docs says:

"We recommend using a dedicated drive for the operating system and software, and one drive for each Ceph OSD Daemon you run on the host."

I could use for example 1 disk for the OS and 11 for OSD data. In the operating system I would run 11 daemons to control the OSDs. But...what happen to the cluster if the disk with the OS fails?? maybe the cluster thinks that 11 OSD failed and try to replicate all that data over the cluster...that sounds no good.

Should I use 2 disks for the OS making a RAID1? in this case I'm "wasting" 8TB only for ~10GB that the OS needs.

In all the docs that i've been reading says ceph has no unique single point of failure, so I think that this scenario must have a optimal solution, maybe somebody could help me.

Thanks in advance.
--
Félix Barbeira.
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