At the moment I am a bit confused about how to configure my journals and where.
I will start my first Ceph-experience with a small home cluster made of two
nodes. Both nodes will get around three to five harddisks and one ssd each. The
harddisks are XFS formated and each one represents an OSD. The ceph pool is
erasure coded(!) and therefore I need a replicated pool on top of it as a cache
tier in order to use block devices. See this diagram for explanation (ASCII):
I Cache Tier: Journal
II Cache Tier: Filestore
+------------+------------+
III OSD1 OSD2 .. OSDn
IV Journal Journal Journal
V Filestore Filestore Filestore
Now I have several journals and settings so that I don't know how to configure
it and where. For each line of the diagram above- where would you place it? On a
harddisk or on the ssd? Does it make sense to store _all_ journals on one SSD?
Does it even make sense to have journals for the OSDs at all as there already is
a journal for the cache tier?
The confusion even gets worse as it comes to harddisk hardware caches (hdparm).
Turn these off? Documentation sounds like this cache is automatically turned off
by newer kernels.
Greetings from germany!
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