Hi openstack list,
I have two problems related to openstack volume service. I really appreciate
your kind reply.
1)Recently, we have measured the volume service performance by selecting the
"tgt" as the target management software.(We use Diablo Openstack and KVM as the
underlying hypervisor)
We created 8 instances, each of which was assigned one iscsi disk from
openstack volume service (RAID0 storage as the LVM volumes with up to 800 MB/s
local sequential READ I/O badnwidth).
These 8 instances were distributed on 8 physical machines, each of which was
assigned 1Gb network bandwidth.
We measured the sequential READ (aio-stress) simultaneously from these 8
instances and identified the total READ I/O bandwidth can only reach up to ~100
MB/s.
We observed the iscsi target was not created in "O_DIRECT" mode, (hard coded in
*/nova/volume/driver.py).
After changing to use "O_DIRECT" mode, by adding "--bsoflags=direct", the
sequential READ I/O bandwidth can reach to ~250 MB/s, greatly improved.
My question is that, why not use "O_DIRECT" mode for "tgt" iscsi target
creation? Is there any special consideration? As I know, another target
management software "iet" created the iscsi target as "O_DIRECT" mode by
default.
Also, we observed that "iet" has better I/O performance than "tgt". We measured
this in 8 native system instead of instances, since our openstack (diablo) does
not support iet.
We added the "O_DIRECT" mode in the following way:
self._execute('tgtadm', '--op', 'new',
'--lld=iscsi', '--mode=logicalunit',
"--tid=%s" % iscsi_target,
'--lun=1',
"--backing-store=%s,Type=fileio" % volume_path,
'--bsoflags=direct',
run_as_root=True)
2)Does Xenserver support volume services? Is there any document to introduce
how to enable volume for Xenserver?
Because, when I attached a volume target to an instance created on Xenserver by
using euca tools, no such iscsi target appeared on the instance. Also there
were no error messages from log files.
Best regards,
Hui
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