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ceph journal

asked 2016-04-07 18:00:38 -0500

senyapsudah gravatar image

Hi Guys,

i'm planning to add more ceph server into our environment. assuming my server has 12 disk for OSD and i have 1 SSD. can someone suggest me the best approach to get my SSD being used as a journal disk for all 12 disk. i understand, the best would be 1SSD for every single disk. since i would like to save a little bit cost on that so i just want to have 1 SSD covers all 12 OSD. i understand the drawback will be causing me loose data if my SSD go down. please advise.


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answered 2016-04-08 00:31:35 -0500

updated 2016-04-08 03:42:27 -0500


A common use case is using SSD as journal, often these journal disks are used by various OSDs, with a recommended relationship of 3-4 OSD per journal disk. 12 OSDs using a single journal SSD disk will result in an imaginable amount of data lost in case of SSD failure. I would not recommend to do that and at least add another SSD into your cluster design to have a 1:6 relationship.

Going back at how to add more that one OSD per journal.

When you create a OSD you need to specify journal disk, that disk can and usually is a partition in the SSD disk.

Prepare the disk selecting a journal disk.

ceph-deploy osd prepare {node-name}:{data-disk}[{:journal-disk}]

Then activate it in a SSD disk partition.

ceph-deploy osd activate {node-name}:{data-disk-partition}[:{journal-disk-partition}]

Also, you can do it with a single command who creates and activate at once, where path to journal can be SSD partition number /dev/ssd1.

ceph-deploy osd create {node-name}:{disk}[:{path/to/journal}]

Adding a recommendation from ceph docs.


When running multiple Ceph OSD daemons on a single node, and sharing a partioned journal with each OSD daemon, you should consider the entire node the minimum failure domain for CRUSH purposes, because if the SSD drive fails, all of the Ceph OSD daemons that journal to it will fail too.


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Asked: 2016-04-07 18:00:38 -0500

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Last updated: Apr 08 '16