Hello,
I need rbd kernel module to really delete data on osd related disks.
Having a ever growing "hidden data" is not a great solution.
Then we can say that first of all we should be able at least manually to
strip out the "hidden" data aka the replicas.
I use rbd image let say it is 10 TB on a overall available space of
25TB. What the real case experience shows me if that if I write in a row
8Tb of my 10 tb. then overall used data is around 18TB. Then I delete
from the rbd image 4TB and write 4 TB then the overall data would grow
from 4 TB, ofcours the pgs used by the rbd image will be reused
overwritten but the replicas corresponding will not so.
in the end after round 2 of writing the overall used space is 22TB
at that moment i get stuff like this:
2034 active+clean
7 active+remapped+wait_backfill+backfill_toofull
7 active+remapped+backfilling
I tried to use ceph osd reweight-by-utilization but that didn t solve
the problem. And if the problem is solve it would be only momentarily
because after cleaning again 4TB and writing 4TB then I will reach the
full ratio and get my osd stucked until I spend 12 000 dollars to
enhance my ceph cluster. Because when you manipulate a 40TB ceph cluster
adding 4TB isn t quite mutch of a difference.
In the end for 40TB of real space 20 disks of 2TB after first formating
I get a 37 TB cluster of available data. Then I do a 18TB rbd image. And
can t use much than 16TB before having my osds showing page stucks.
In the end 37TB for a 16TB of available disk space for sometimes is
quite not the great solution at all because I loose 60% of my data
storage.
On the how to delete data, really I don't know the more "easy" way
I can see is at least to be able to manually tell rbd kernel module to
clean "released" data from osd when we see it fit "maintenance time".
If doing it automatically has a too bad impact on overall performances.
I would be glad yet to be able to decide an appropriate moment to force
cleaning task that would be better than nothing and ever growing "hiden"
data situation.
Regards,
--
Alphe Salas
I.T ingeneer
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