[linux-lvm] poor read performance on rbd+LVM, LVM overload

Ugis ugis22 at gmail.com
Fri Oct 18 07:56:57 UTC 2013

> Ugis, please provide the output of:
> RBD_DEVICE=<rbd device name>
> pvs -o pe_start $RBD_DEVICE
> cat /sys/block/$RBD_DEVICE/queue/minimum_io_size
> cat /sys/block/$RBD_DEVICE/queue/optimal_io_size
> The 'pvs' command will tell you where LVM aligned the start of the data
> area (which follows the LVM metadata area).  Hopefully it reflects what
> was published in sysfs for rbd's striping.

output follows:
#pvs -o pe_start /dev/rbd1p1
  1st PE
# cat /sys/block/rbd1/queue/minimum_io_size
# cat /sys/block/rbd1/queue/optimal_io_size

Seems correct in terms of ceph-LVM io parameter negotiation? I wonded
about gpt header+PV metadata - it makes some shift starting from ceph
1st block beginning. Does this mean that all following LVM 4m data
blocks are shifted by this part and span 2 ceph objects?
If so, performance will be affected.


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