Am 12.11.2012 15:42, schrieb Sage Weil:
On Sun, 11 Nov 2012, Stefan Priebe wrote:
Hi Sage,
With btrfs, yes, although this isn't something we have tested in a while.
I'm not using btrfs as long as the devs claim it is not ready for prod.
In that case, the journal is needed for consistency of the fs; we rely on
writeahead journaling. It can't be turned off.
Putting it on a ramdisk in this case is interesting for performance, but
it means that a crash/reboot/powerloss event leaves the fs in an
inconsistent and unusable state.
But only if for replicas 2 both nodes crash / have a powerloss?
The only time tmpfs is potentially useful in production is when you're
using btrfs *and* have independent backup power sources for replicas (and
can thus avoid worrying about a site-wide power failure and loss of
journal). (Or have relaxed requirements for the durability of recent
writes.)
What happens for XFS and replicas two and ONE host has a power loss? The
other replica / journal should be still there.
I've no idea where to put the journal on.
I mean i've 8 SSDs per Host one per osd each with a write IOP/s speed of
45.000 iops to whole IOP/s write speed of 360.000 IOP/s per Node.
Which journal device can handle this? And if i put the journal on the
same disk as the OSD it has to copy the data around.
Greets,
Stefan
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