We've done the splitting several times. The most important thing is to
run a ceph version which does not have the linger ops bug.
This is dumpling latest release, giant and hammer. Latest firefly
release still has this bug. Which results in wrong watchers and no
working snapshots.
Stefan
Am 04.08.2015 um 18:46 schrieb Samuel Just:
It will cause a large amount of data movement. Each new pg after the
split will relocate. It might be ok if you do it slowly. Experiment
on a test cluster.
-Sam
On Mon, Aug 3, 2015 at 12:57 AM, 乔建峰 <scaleqiao@xxxxxxxxx> wrote:
Hi Cephers,
This is a greeting from Jevon. Currently, I'm experiencing an issue which
suffers me a lot, so I'm writing to ask for your comments/help/suggestions.
More details are provided bellow.
Issue:
I set up a cluster having 24 OSDs and created one pool with 1024 placement
groups on it for a small startup company. The number 1024 was calculated per
the equation 'OSDs * 100'/pool size. The cluster have been running quite
well for a long time. But recently, our monitoring system always complains
that some disks' usage exceed 85%. I log into the system and find out that
some disks' usage are really very high, but some are not(less than 60%).
Each time when the issue happens, I have to manually re-balance the
distribution. This is a short-term solution, I'm not willing to do it all
the time.
Two long-term solutions come in my mind,
1) Ask the customers to expand their clusters by adding more OSDs. But I
think they will ask me to explain the reason of the imbalance data
distribution. We've already done some analysis on the environment, we
learned that the most imbalance part in the CRUSH is the mapping between
object and pg. The biggest pg has 613 objects, while the smallest pg only
has 226 objects.
2) Increase the number of placement groups. It can be of great help for
statistically uniform data distribution, but it can also incur significant
data movement as PGs are effective being split. I just cannot do it in our
customers' environment before we 100% understand the consequence. So anyone
did this under a production environment? How much does this operation affect
the performance of Clients?
Any comments/help/suggestions will be highly appreciated.
--
Best Regards
Jevon
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