On 09/09/2014 07:06 AM, yuelongguang wrote: > hi, josh.durgin: > i want to know how librbd launch io request. > use case: > inside vm, i use fio to test rbd-disk's io performance. > fio's pramaters are bs=4k, direct io, qemu cache=none. > in this case, if librbd just send what it gets from vm? i mean no > gather/scatter. the rate , io inside vm : io at librbd: io at osd > filestore = 1:1:1? If the rbd image is not a clone, the io issued from the vm's block driver will match the io issued by librbd. With caching disabled as you have it, the io from the OSDs will be similar, with some small amount extra for OSD bookkeeping.
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