[pve-devel] multipath problems

[Dietmar Maurer]

Hi all,

I am just setting up a nexenta storage (community edition) and try to use multipath on the proxmox side:

# multipath -l
mpath1 (3600144f0001e58febc44503399600001) dm-3 NEXENTA,NEXENTASTOR
size=100G features='1 queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=-3 status=active
  |- 5:0:0:0 sdd 8:48 active undef running
  |- 3:0:0:0 sdb 8:16 active undef running
  `- 4:0:0:0 sdc 8:32 active undef running

I assume above output is OK so far.

The strange thing is that we get very poor performance. When I test a
single iscsi drive I get:

# hdparm -t /dev/sdc

/dev/sdc:
Timing buffered disk reads: 338 MB in  3.00 seconds = 112.48 MB/sec
root at dell1:~# hdparm -t /dev/sdb

/dev/sdb:
Timing buffered disk reads: 222 MB in  3.01 seconds =  73.69 MB/sec
root at dell1:~# hdparm -t /dev/sdd

/dev/sdd:
Timing buffered disk reads: 262 MB in  3.01 seconds =  87.07 MB/sec

When I test the multipath drive I get:

# hdparm -t /dev/mapper/mpath1

/dev/mapper/mpath1:
Timing buffered disk reads: 266 MB in  3.02 seconds =  88.04 MB/sec

So there is no speed gain. I already checked that traffic is routed to different network cards.
Any idea why it is that slow?

- Dietmar


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