So you need to think about failure domains.
Failure domains will be set to host.
If you put all the DB's on one SSD and all the
WAL's on another SSD then a failure of either of those SSD's will result in a
failure of all the OSD's behind them. So in this case all 10 OSD's would have
Splitting it to 5 OSD's you have RocksDb and WAL on each SSD this then results in a
failure of an SSD only impacting 5 OSD's.
A failure of an SSD will take down all the OSD's that are behind that SSD.
That is what I wondered, thanks to confirm it.
That's one of the reasons I would always say you
need 1 nodes worth of spare capacity in the cluster to allow for automated re-builds to
As for your EC 7+5 I would have gone for some thing like 8+3 as then you have a spare
node active in the cluster and can still provide full protection in the event of a failure
of a node.
Make sense! On another cluster, I have an EC 7+5 pool for cephfs but there are 4 servers
per chassis. In case I lost one chassis, I still need
to access data. But for that cluster, you are right, 8+3 may be enough for redundancy.
Think about software updates that require a reboot of
a node. Any data written during that time will need recovering to bring it back to full
protection where as if you have a spare node then that data could be written and not
require a later recovery.
It is mostly a read-only cluster to distribute public datasets over S3 inside our network,
it is fine for me if write operations are not fully
protected during a couple of days. All writes operations are managed by us to update
But as mentioned above, 8+3 may be a good compromise.
On 03/09/2019, 10:29, "Yoann Moulin"
I am deploying a new Nautilus cluster and I would like to know what would be the best
OSD's scenario config in this case :
10x 6TB Disk OSDs (data)
2x 480G SSD previously used for journal and can be used for WAL and/or DB
Is it better to put all WAL on one SSD and all DBs on the other one? Or put WAL and
DB of the first 5 OSDs on the first SSD and the 5 others on
the second one.
A more general question, what is the impact on an OSD if we lose the WAL? The DB?
I plan to use EC 7+5 on 12 servers and I am OK if I lose one server temporarily. I
have spare servers and I can easily add another one in this
To deploy this cluster, I use ceph-ansible (stable-4.0). I am not sure how to
configure the playbook to use SSD and disks with LVM.
Is this good?
- data: data-lv1
- data: data-lv2
Is it possible to let the playbook configure LVM for each disk in a mixed case? It
looks like I must configure LVM before running the playbook
but I am not sure if I missed something.
Is wal_vg and db_vg can be identical (on VG per SSD shared with multiple OSDs)?
Thanks for your help.
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