Re: poor OSD performance using kernel 3.4

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

Am 28.05.2012 07:37, schrieb Alexandre DERUMIER:
> I think filestore journal parallel works only with btrfs.
> Other filesystem are writeahead.
... you might be right but i can't change ceph's implementation.

> if you write at 120MB/S, so your journal of 1GB is at 50% in 4sec.
>
> So you got around 480MB each 4sec, does your disks can flush sequentially these 480MB in less than 4sec ?
> (do a small benchmark of your disk in local filesystem, without ceph)
>
> If not, you can have spikes in your write stats if the journal.
>
> simple schema if disks are not fast enough:
I totally aggree with you but this is just a test setup AND if you have 
a big log file to copy let's say 100GB your journal will never be big 
enough and the speed should never drop to 0MB/s. Also i see the correct 
behaviour with 3.0.X where the speed is maxed to the underlying device. 
So i still see no reason that with 3.4 the speed drops to 0MB/s and is 
mostly 10-20MB/s instead of 130MB/s.

> How many disks (7,2K) do you have by osd ?
One intel 520 SSD per OSD.

Stefan