Am 28.06.2012 18:12, schrieb Josh Durgin:
On 06/28/2012 06:10 AM, Stefan Priebe - Profihost AG wrote:
Hello list,
my cluster is now pretty stable i'm just wondering about the sequential
write values.
With rados bench command and 16 threads i get totally different values
than with KVM and rbd block device.
rados -p kvmpool bench 60 write -t 16:
pool size 2: Bandwidth (MB/sec): 1137.294
pool size 3: Bandwidth (MB/sec): 846.983
Inside KVM with fio:
fio --filename=$DISK --direct=1 --rw=write --bs=4M --size=200G
--numjobs=16 --runtime=60 --group_reporting --name=file1:
There are a number of differences between running that in a vm on rbd
and rados bench.
Keep in mind it's running on a filesystem, so requests go through the
guest fs and block layer before getting into librbd.
No it doesn't i'm testing directly the block device.
If you don't use direct I/O, and you enable rbd writeback caching,
librbd will be able to merge many of the smaller requests and
you should see much better throughput.
I'm already using rbd writeback and it works good for random 4k writes,
But it doesn't make sense for sequential 4M writes.
Stefan
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