Hello,
On 10/31/2012 10:24 PM, Tren Blackburn wrote:
On Wed, Oct 31, 2012 at 2:18 PM, Gandalf Corvotempesta
<gandalf.corvotempesta@xxxxxxxxx> wrote:
In a multi replica cluster (for example, replica = 3) is safe to set
journal on a tmpfs?
As fa as I understood with journal enabled all writes are wrote on
journal and then to disk in a second time.
If node hangs when datas are still on journal (and journal is not on a
permanent disk), some data lost could happens.
In a multi replica environment, other nodes should be able to write
the same datas to disk, right? I this case, using a journal on a tmpfs
should be safe enough.
Unless you're using btrfs which writes to the journal and osd fs
concurrently, if you lose the journal device (such as due to a
reboot), you've lost the osd device, requiring it to be remade and
re-added.
This is what I understand at least. If I'm wrong one of the devs will
strike me down I'm sure ;)
There's an option to recreate the journal, so you don't lose the OSD.
Ofcourse you lose the data in the journal.
It's possible to have the journal on a tmpfs device, ofcourse it's not
100% safe, in case you lose the three nodes with the replica's you can
lose data. But then again if you have more replica's the change of
losing them all gets smaller. It's a trade between speed, reliability
and space.
Stefan
--
To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
