Re: ceph data not well distributed.

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On Tue, 14 Apr 2015, Mark Nelson wrote:
> On 04/14/2015 08:58 PM, Yujian Peng wrote:
> > I have a ceph cluster with 125 osds with the same weight.
> > But I found that data is not well distributed.
> > df
> > Filesystem          1K-blocks      Used Available Use% Mounted on
> > /dev/sda1            47929224   2066208  43405264   5% /
> > udev                 16434372         4  16434368   1% /dev
> > tmpfs                 6578584       728   6577856   1% /run
> > none                     5120         0      5120   0% /run/lock
> > none                 16446460         0  16446460   0% /run/shm
> > /dev/sda6              184307     62921    107767  37% /boot
> > /dev/mapper/osd-104 877797376 354662904 523134472  41% /ceph-osd/osd-104
> > /dev/mapper/osd-105 877797376 596911248 280886128  69% /ceph-osd/osd-105
> > /dev/mapper/osd-106 877797376 497968080 379829296  57% /ceph-osd/osd-106
> > /dev/mapper/osd-107 877797376 640225368 237572008  73% /ceph-osd/osd-107
> > /dev/mapper/osd-108 877797376 509972412 367824964  59% /ceph-osd/osd-108
> > /dev/mapper/osd-109 877797376 581435864 296361512  67% /ceph-osd/osd-109
> > /dev/mapper/osd-110 877797376 724248740 153548636  83% /ceph-osd/osd-110
> > /dev/mapper/osd-111 877797376 495883796 381913580  57% /ceph-osd/osd-111
> > /dev/mapper/osd-112 877797376 488635912 389161464  56% /ceph-osd/osd-112
> > /dev/mapper/osd-113 877797376 613807596 263989780  70% /ceph-osd/osd-113
> > /dev/mapper/osd-114 877797376 633144408 244652968  73% /ceph-osd/osd-114
> > /dev/mapper/osd-115 877797376 519702956 358094420  60% /ceph-osd/osd-115
> > /dev/mapper/osd-116 877797376 449834752 427962624  52% /ceph-osd/osd-116
> > /dev/mapper/osd-117 877797376 641484036 236313340  74% /ceph-osd/osd-117
> > /dev/mapper/osd-118 877797376 519416488 358380888  60% /ceph-osd/osd-118
> > /dev/mapper/osd-119 877797376 599926788 277870588  69% /ceph-osd/osd-119
> > /dev/mapper/osd-120 877797376 460384476 417412900  53% /ceph-osd/osd-120
> > /dev/mapper/osd-121 877797376 646286724 231510652  74% /ceph-osd/osd-121
> > /dev/mapper/osd-122 877797376 647260752 230536624  74% /ceph-osd/osd-122
> > /dev/mapper/osd-123 877797376 432367436 445429940  50% /ceph-osd/osd-123
> > /dev/mapper/osd-124 877797376 595846772 281950604  68% /ceph-osd/osd-124
> > 
> > The osd.104 is 41% full, but osd.110 is 83%.
> > Can I move some pgs from osd.110 to osd.104 manually?
> 
> No, but if your pools have a low number of PGs for the number of OSDs you have
> you may see poor distribution quality.  You can increase the number of PGs in
> your pool(s) which may result in better data distribution.  You may be
> interested in a script we created that will show you statistics about how your
> PGs are currently distributed:
> 
> https://github.com/ceph/cbt/blob/master/tools/readpgdump.py
> 
> You can run it like: ceph pg dump | readpgdump.py

Once you have more PGs, you can do

 ceph osd reweight-by-utilization

to automatically adjust things to improve the balance.

sage

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