[PVE-User] LVM over ISCSI Bad performance

Harald Leithner leithner at itronic.at
Tue Jun 21 19:15:07 CEST 2016


Hi,

I have a MSA2312 connected with 1gbit to a 3 node PVE 4.2 Cluster.
I managed to get ISCSI and LVM working and attached it to a VM.

Atm I didn't manage to get multipath working with PVE because the 
Wikipage tells me how to create multipath (which works) but not how PVE 
uses it for LVM VGs... maybe someone give me a hint.

Anyway the main problem is that fio only gives me a read performance of 
5 mb/s if I attach a disk as virtio or scsi device with cache "Writeback".

If I attach the same SAN Drive directly in the VM with iSCSI (with and 
without multipath) I get about 112 MB/s.

I also get this speed on the pve host.

I use:

fio --filename=/dev/sdb --direct=1 --rw=read --bs=1m --size=20G 
--numjobs=200 --runtime=60 --group_reporting --name=file1

for benchmarking.

While benchmarking the VM I see 1300% cpu usage on the host (mainly sys 
time)

Maybe someone has a idea?

regards

-- 
Harald Leithner

ITronic
Wiedner Hauptstra├če 120/5.1, 1050 Wien, Austria
Tel: +43-1-545 0 604
Mobil: +43-699-123 78 4 78
Mail: leithner at itronic.at | itronic.at



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