On 07/03/2014 08:11 AM, VELARTIS Philipp Dürhammer wrote:
Hi,
I have a ceph cluster setup (with 45 sata disk journal on disks) and get
only 450mb/sec writes seq (maximum playing around with threads in rados
bench) with replica of 2
Which is about ~20Mb writes per disk (what y see in atop also)
theoretically with replica2 and having journals on disk should be 45 X
100mb (sata) / 2 (replica) / 2 (journal writes) which makes it 1125
satas in reality have 120mb/sec so the theoretical output should be more.
I would expect to have between 40-50mb/sec for each sata disk
Can somebody confirm that he can reach this speed with a setup with
journals on the satas (with journals on ssd speed should be 100mb per disk)?
or does ceph only give about ¼ of the speed for a disk? (and not the ½
as expected because of journals)
My setup is 3 servers with: 2 x 2.6ghz xeons, 128gb ram 15 satas for
ceph (and ssds for system) 1 x 10gig for external traffic, 1 x 10gig for
osd traffic
with reads I can saturate the network but writes is far away. And I
would expect at least to saturate the 10gig with sequential writes also
In addition to the advice wido is providing (which I wholeheartedly
agree with!), you might want to check your controller/disk
configuration. If you have journals on the same disks as the data, some
times putting the disks into single-disk RAID0 LUNs with writeback cache
enabled can help keep journal and data writes from causing seek
contention. This only works if you have a controller with cache and a
battery though.
Thank you
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