Re: Disabling journal

[Stefan Priebe - Profihost AG <s.priebe@profihost.ag>]

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