Re: Cache Tiering Question

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Hello,

Having run into this myself two days ago (setting relative sizing values
doesn't flush things when expected) I'd say that the documentation is
highly misleading when it comes to the relative settings.

And unclear when it comes to the size/object settings.

Guess this section needs at least one nice red paragraph and some further
explanations.

Christian

On Thu, 15 Oct 2015 17:33:30 -0600 Robert LeBlanc wrote:

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> One more question. Is max_{bytes,objects} before or after replication
> factor?
> - ----------------
> Robert LeBlanc
> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904  C70E E654 3BB2 FA62 B9F1
> 
> 
> On Thu, Oct 15, 2015 at 4:42 PM, LOPEZ Jean-Charles  wrote:
> > Hi Robert,
> >
> > yes they do.
> >
> > Pools don’t have a size when you create them hence the couple
> > value/ratio that is to be defined for cache tiering mechanism. Pool
> > only have a number of PGs assigned. So setting the max values and the
> > ratios for dirty and full must be set explicitly to match your
> > configuration.
> >
> > Note that you can at the same time define max_bytes and max_objects.
> > The first of the 2 values that breaches using your ratio settings will
> > trigger eviction and/or flushing. The ratios you choose apply to both
> > values.
> >
> > Cheers
> > JC
> >
> >> On 15 Oct 2015, at 15:02, Robert LeBlanc  wrote:
> >>
> >> -----BEGIN PGP SIGNED MESSAGE-----
> >> Hash: SHA256
> >>
> >> hmmm...
> >>
> >> http://docs.ceph.com/docs/master/rados/operations/cache-tiering/#relative-sizing
> >>
> >> makes it sound like it should be based on the size of the pool and
> >> that you don't have to set anything like max bytes/objects. Can you
> >> confirm that cache_target_{dirty,dirty_high,full}_ratio works as a
> >> ratio of target_max_bytes set?
> >> - ----------------
> >> Robert LeBlanc
> >> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904  C70E E654 3BB2 FA62 B9F1
> >>
> >>
> >> On Thu, Oct 15, 2015 at 3:32 PM, Nick Fisk  wrote:
> >>>
> >>>
> >>>
> >>>
> >>>> -----Original Message-----
> >>>> From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On
> >>>> Behalf Of Robert LeBlanc
> >>>> Sent: 15 October 2015 22:06
> >>>> To: ceph-users@xxxxxxxxxxxxxx
> >>>> Subject:  Cache Tiering Question
> >>>>
> >>>> -----BEGIN PGP SIGNED MESSAGE-----
> >>>> Hash: SHA256
> >>>>
> >>>> ceph df (ceph version 0.94.3-252-g629b631
> >>>> (629b631488f044150422371ac77dfc005f3de1bc)) is showing some odd
> >>>> results:
> >>>>
> >>>> root@nodez:~# ceph df
> >>>> GLOBAL:
> >>>>    SIZE       AVAIL      RAW USED     %RAW USED
> >>>>    24518G     21670G        1602G          6.53
> >>>> POOLS:
> >>>>    NAME         ID     USED      %USED     MAX AVAIL     OBJECTS
> >>>>    rbd          0      2723G     11.11         6380G     1115793
> >>>>    ssd-pool     2          0         0          732G           1
> >>>>
> >>>> The rbd pool is showing 11.11% used, but if you calculate the
> >>>> numbers
> >>> there
> >>>> it is 2723/6380=42.68%.
> >>>
> >>> I have a feeling that the percentage is based on the amount used of
> >>> the total cluster size. Ie 2723/24518
> >>>
> >>>>
> >>>> Will this cause problems with the relative cache tier settings? Do
> >>>> I need
> >>> to set
> >>>> the percentage based on what Ceph is reporting here?
> >>>
> >>> The flushing/eviction thresholds are based on the target_max_bytes
> >>> number that you set, they have nothing to do with the underlying
> >>> pool size. It's up to you to come up with a sane number for this
> >>> variable.
> >>>
> >>>>
> >>>> Thanks,
> >>>> - ----------------
> >>>> Robert LeBlanc
> >>>> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904  C70E E654 3BB2 FA62 B9F1
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> >>>
> >>>
> >>
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> >> =cI+5
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> >
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> =de2k
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-- 
Christian Balzer        Network/Systems Engineer                
chibi@xxxxxxx   	Global OnLine Japan/Fusion Communications
http://www.gol.com/
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