Re: 10 times higher disk load with btrfs

[Mark Nelson <mark.nelson@inktank.com>]

On 01/05/2015 02:20 PM, Stefan Priebe wrote:
> Hi Sage,
>
> Am 05.01.2015 um 20:25 schrieb Sage Weil:
>> On Mon, 5 Jan 2015, Stefan Priebe wrote:
>>>
>>> Am 05.01.2015 um 19:36 schrieb Stefan Priebe:
>>>> Hi devs,
>>>>
>>>> while btrfs is now declared as stable ;-) i wanted to retest btrfs on
>>>> our production cluster on 2 out of 54 osds. So if they crash it doesn't
>>>> hurt.
>>>>
>>>> While if those OSDs run XFS have spikes of 20MB/s every 4-7s. The same
>>>> OSDs after formatting them with btrfs have spikes of 190MB/s every
>>>> 4-7s.
>>>>
>>>> Why does just another filesystem raises the disk load by a factor of
>>>> 10?
>>>
>>> OK this seems to happen cause ceph is creating every 5s a new
>>> subvolume /
>>> snap. Is this really expected / needed?
>>
>> You can disable it with
>>
>>   filestore btrfs snap = false
>>
>> I'm curious how much this drops the load down; originally the
>> snaps were no more expensive than a regular sync but perhaps this
>> has changed...
>
> - with XFS the average write is at 9Mb/s
> - with btrfs (filestore_btrfs_snap=true) write is at 40Mb/s
> - with btrfs (filestore_btrfs_snap=false) write is at 20Mb/s

Is that the average and not the spikes?  It looks like before the spikes 
were 20MB/s and 190MB/s?

>
> Stefan
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