Hi,everyone
recently,I want to migrate our on-line cluster from straw to
straw2,because if I add or remove some osds,too much objects are to be
replaced than it should be.
I have a confusing in using straw2, because straw2 should have a
character that if an item's weight was adjusted up or down, mappings
would either
move to or from the adjusted item, but never between other unmodified
items in the bucket.
However after I do the test below , I still find pgs move from
unmodified items,I am not sure whether this is normal.
code from :commit 1113eb6b98cb8224f8c3e407435923de7415ca3f
Step1:MON=1 OSD=6 ./vstart.sh -l -n -x
Step2:[root@localhost src]# ./ceph osd pool create newpool 200 200
Step3:[root@localhost src]# ./ceph osd getcrushmap -o crush.out
Step4:[root@localhost src]# ./crushtool -d crush.out -o crush.txt
Step5:[root@localhost src]# vi crush.txt //modify crush map
=======================================================================
# buckets
host localhost {
id -2 # do not change unnecessarily
# weight 18.000
alg straw2
hash 0 # rjenkins1
item osd.0 weight 2.000
item osd.1 weight 2.000
item osd.2 weight 3.000
item osd.3 weight 3.000
item osd.4 weight 4.000
item osd.5 weight 4.000
}
root default {
id -1 # do not change unnecessarily
# weight 18.000
alg straw
hash 0 # rjenkins1
item localhost weight 6.000
}
===============================================================================
Step6:[root@localhost src]# ./crushtool -c crush.txt -o crush.out
Step7:[root@localhost src]# ./crushtool -i crush.out --test --min-x 1
--max-x 1000 --num-rep 3 --show-statistics --show-mappings >straw.old
Step8:[root@localhost src]# ./crushtool -i crush.out --reweight-item
osd.5 0 -o crush.out.new
Step9:[root@localhost src]# ./crushtool -i crush.out.new --test
--min-x 1 --max-x 1000 --num-rep 3 --show-statistics --show-mappings
>straw.new
Step9:[root@localhost src]# diff -y --suppress-common-lines straw.old
straw.new >straw.diff
In straw.diff we can find pg movements like：
old new
CRUSH rule 0 x 453 [5,2,1] CRUSH rule 0 x 453 [0,2,4]
CRUSH rule 0 x 628 [3,0,5] CRUSH rule 0 x 628 [3,0,2]
CRUSH rule 0 x 629 [3,1,0] CRUSH rule 0 x 629 [3,5,1]
CRUSH rule 0 x 759 [5,2,1] CRUSH rule 0 x 759 [0,4,3]
Conclusion:
If the osd.5 is the primary osd,or second osd in a pg, then other osd
behind osd.5 are still possible to be switched out,Is this what straw2
really want achieve?
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