Re: osd: new pool flags: noscrub, nodeep-scrub

[Wido den Hollander <wido@42on.com>]

On 11-09-15 15:11, Sebastien Han wrote:
> I like the idea of being able to control on which pool we want to run scrub on.
> Some data might deserve better protection than others, it’s really up to the admin.
> 

Indeed. Let the admin be in control. If he/she doesn't want that pool to
be scrubbed Ceph shouldn't care.

Same like you can mount a filesystem with nobarrier if you want to. Not
that it is a wise thing to do.

> The default behaviour will be to apply scrub to default pool and every new created pools.
> The operator can change this behaviour either with a config flag or directly with a ceph mon command.
> 
>> On 11 Sep 2015, at 14:59, Sage Weil <sweil@redhat.com> wrote:
>>
>> On Fri, 11 Sep 2015, Mykola Golub wrote:
>>> On Fri, Sep 11, 2015 at 11:08:29AM +0100, Gregory Farnum wrote:
>>>> On Fri, Sep 11, 2015 at 7:42 AM, Mykola Golub <mgolub@mirantis.com> wrote:
>>>>> Hi,
>>>>>
>>>>> I would like to add new pool flags: noscrub and nodeep-scrub, to be
>>>>> able to control scrubbing on per pool basis. In our case it could be
>>>>> helpful in order to disable scrubbing on cache pools, which does not
>>>>> work well right now, but I can imagine other scenarios where it could
>>>>> be useful too.
>>>>
>>>> Can you talk more about this? It sounds to me like maybe you dislike
>>>> the performance impact of scrubbing, but it's fairly important in
>>>> terms of data integrity. I don't think we want to permanently disable
>>>> them. A corruption in the cache pool isn't any less important than in
>>>> the backing pool ? it will eventually get flushed, and it's where all
>>>> the reads will be handled!
>>>
>>> I was talking about this:
>>>
>>> http://tracker.ceph.com/issues/8752
>>>
>>> (false-negative on a caching pool). Although the best solution is
>>> definitely to fix the bug, I am not sure it will be resolved soon (the
>>> bug is open for a year). Still these false-negatives are annoying, as
>>> they complicate monitoring for real inconsistent pgs. In this case I
>>> might want to disable periodic scrub for caching pools, as a
>>> workaround (I could do scrub for them manually though).
>>>
>>> This might be not the best example where these flags could be helpful
>>> (I just came to the idea when thinking about a workaround for that
>>> problem, and this looked useful to me in general). We already have
>>> 'ceph osd set no[deep-]scrub', and users use it to temporary resolve
>>> high I/O load. Being able to do this per pool looks useful too.
>>>
>>> You might have pools of different importance for you, and disabling
>>> scrub for some of them might be ok.
>>
>> I wonder if, in addition, we should also allow scrub and deep-scrub
>> intervals to be set on a per-pool basis?
>>
>> sage
>>
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> 
> 
> Cheers.
> ––––
> Sébastien Han
> Senior Cloud Architect
> 
> "Always give 100%. Unless you're giving blood."
> 
> Mail: seb@redhat.com
> Address: 11 bis, rue Roquépine - 75008 Paris
> 
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