Hi,
We test sync iops with fio sync=1 for database workloads in VM,
the backend is librbd and ceph (all SSD setup).'
The result is sad to me. we only get ~400 IOPS sync randwrite with iodepth=1
to iodepth=32.
But test in physical machine with fio ioengine=rbd sync=1, we can
reache ~35K IOPS.
seems the qemu rbd is the bottleneck.
qemu version is 2.1.2 with rbd_aio_flush patched.
rbd cache is off, qemu cache=none.
IMHO, ceph use sync write for every write to disk, so
rbd_aio_flush can ignore the sync
cache command if rbd cache is off so that we can get higher
iops(similar to direct=1 write)
for sync=1 iops, right?
Very appreciated to get your reply!
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