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I'm desperately trying to improve performance of my SAN connection.

Here's what i have:

[root@xnode1 dell]# multipath -ll
mpath1 (36d4ae520009bd7cc0000030e4fe8230b) dm-2 DELL,MD36xxi
[size=5.5T][features=3 queue_if_no_path pg_init_retries 50][hwhandler=1 rdac][rw]
\_ round-robin 0 [prio=200][active]
 \_ 18:0:0:0  sdb 8:16  [active][ready]
 \_ 19:0:0:0  sdd 8:48  [active][ghost]
 \_ 20:0:0:0  sdf 8:80  [active][ghost]
 \_ 21:0:0:0  sdh 8:112 [active][ready]

And multipath.conf :

defaults {
    udev_dir        /dev
    polling_interval    5
    prio_callout        none
    rr_min_io       100
    max_fds         8192
    user_friendly_names yes
    path_grouping_policy    multibus
    default_features    "1 fail_if_no_path"
}
blacklist {
    device {
               vendor "*"
        product "Universal Xport"
        }
}
devices {
    device {
           vendor "DELL"
           product "MD36xxi"
           path_checker rdac
           path_selector "round-robin 0"
           hardware_handler "1 rdac"
           failback immediate
           features "2 pg_init_retries 50"
           no_path_retry 30
           rr_min_io 100
           prio_callout "/sbin/mpath_prio_rdac /dev/%n"
       }
}

And sessions.

[root@xnode1 dell]# iscsiadm  -m session
tcp: [13] 10.0.51.220:3260,1 iqn.1984-05.com.dell:powervault.md3600i.6d4ae520009bd7cc000000004fd7507c
tcp: [14] 10.0.50.221:3260,2 iqn.1984-05.com.dell:powervault.md3600i.6d4ae520009bd7cc000000004fd7507c
tcp: [15] 10.0.51.221:3260,2 iqn.1984-05.com.dell:powervault.md3600i.6d4ae520009bd7cc000000004fd7507c
tcp: [16] 10.0.50.220:3260,1 iqn.1984-05.com.dell:powervault.md3600i.6d4ae520009bd7cc000000004fd7507c

I'm getting very poor read performance :

dd if=/dev/mapper/mpath1 of=/dev/null bs=1M count=1000

The SAN is configured as follows:

   CTRL0,PORT0 : 10.0.50.220
   CTRL0,PORT1 : 10.0.50.221
   CTRL1,PORT0 : 10.0.51.220
   CTRL1,PORT1 : 10.0.51.221

And on the host :

   IF0 : 10.0.50.1
   IF1 : 10.0.51.1

(Dual 10GbE Ethernet Card Intel DA2)

It's connected to a 10gbE switch dedicated for SAN traffic.

My questions being; why the connection is set up as 'ghost' and not 'ready' like an active/active configuration ?

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As I answered in the other question, it might be your disks, and we need more information. –  Basil Jul 1 '12 at 0:26
    

1 Answer 1

The Dell MD series are all LSI clones (like entry level IBM DS boxes), and thus use RDAC for multipathing. RDAC is an A/P multipath mechanism, there's nothing you can do about it.

Note, I haven't used MD3600 yet, but the statement is true for 3000 and 3200 series, and I doubt anything changed except for some extra specs (like the switch to 10GigE)

EDIT: apparently it is possible to switch to active/active now, best to call Dell techsupport for a walkthrough

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