Re: RBD fio Performance concerns

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

Am 22.11.2012 16:26, schrieb Alexandre DERUMIER:
>>> Haven't tested that. But does this makes sense? I mean data goes to Disk
>>> journal - same disk then has to copy the Data from part A to part B.
>>>
>>> Why is this an advantage?
>
> Well, if you are cpu limited, I don't think you can use all 8*35000iops by node.
> So, maybe a benchmark can tell us if the difference is really big.
>
> Using tmpfs and ups can be ok, but if you have a kernel panic or hardware problem, you'll lost your journal.

But who cares? it's also on the 2nd node. or even on the 3rd if you have 
replicas 3.

Stefan


> ----- Mail original -----
>
> De: "Stefan Priebe - Profihost AG" <s.priebe@profihost.ag>
> À: "Mark Nelson" <mark.nelson@inktank.com>
> Cc: "Alexandre DERUMIER" <aderumier@odiso.com>, "ceph-devel" <ceph-devel@vger.kernel.org>, "Mark Kampe" <mark.kampe@inktank.com>, "Sébastien Han" <han.sebastien@gmail.com>
> Envoyé: Jeudi 22 Novembre 2012 16:01:56
> Objet: Re: RBD fio Performance concerns
>
> Am 22.11.2012 15:46, schrieb Mark Nelson:
>> I haven't played a whole lot with SSD only OSDs yet (other than noting
>> last summer that iop performance wasn't as high as I wanted it). Is a
>> second partition on the SSD for the journal not an option for you?
>
> Haven't tested that. But does this makes sense? I mean data goes to Disk
> journal - same disk then has to copy the Data from part A to part B.
>
> Why is this an advantage?
>
> Stefan
>
>> Mark
>>
>> On 11/22/2012 08:42 AM, Stefan Priebe - Profihost AG wrote:
>>> Am 22.11.2012 15:37, schrieb Mark Nelson:
>>>> I don't think we recommend tmpfs at all for anything other than playing
>>>> around. :)
>>>
>>> I discussed this with somebody frmo inktank. Had to search the
>>> mailinglist. It might be OK if you're working with enough replicas and
>>> UPS.
>>>
>>> I see no other option while working with SSDs - the only Option would be
>>> to be able to deaktivate the journal at all. But ceph does not support
>>> this.
>>>
>>> Stefan
>>>
>>>> On 11/22/2012 08:22 AM, Stefan Priebe - Profihost AG wrote:
>>>>> Hi,
>>>>>
>>>>> can someone from inktank comment this? Might be using /dev/ram0 with an
>>>>> fs on it be better than tmpfs as we can use dio?
>>>>>
>>>>> Greets,
>>>>> Stefan
>>>>>
>>>>>> ----- Mail original -----
>>>>>>
>>>>>> De: "Stefan Priebe - Profihost AG" <s.priebe@profihost.ag>
>>>>>> À: "Sébastien Han" <han.sebastien@gmail.com>
>>>>>> Cc: "Mark Nelson" <mark.nelson@inktank.com>, "Alexandre DERUMIER"
>>>>>> <aderumier@odiso.com>, "ceph-devel" <ceph-devel@vger.kernel.org>,
>>>>>> "Mark Kampe" <mark.kampe@inktank.com>
>>>>>> Envoyé: Jeudi 22 Novembre 2012 14:29:03
>>>>>> Objet: Re: RBD fio Performance concerns
>>>>>>
>>>>>> Am 22.11.2012 14:22, schrieb Sébastien Han:
>>>>>>> And RAMDISK devices are too expensive.
>>>>>>>
>>>>>>> It would make sense in your infra, but yes they are really expensive.
>>>>>>
>>>>>> We need something like tmpfs - running in local memory but support
>>>>>> dio.
>>>>>>
>>>>>> Stefan
>>>>>>
>>>>
>>>>
>>
>>
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