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Replies:
2
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Last Post:
Nov 4, 2009 11:02 PM
by: acheal
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Posts:
18
From:
Registered:
6/24/09
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Multipath (mpxio) needed on SAS or not?
Posted:
Oct 11, 2009 12:06 PM
To: Communities » storage » discuss
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Given the following:
- I have two-port SAS HBA (LSI3801E) and a generic 23 disk JBOD with two external interfaces
- If I plug one port of the SAS HBA to either port of the JBOD, I see all 23 disks in "format"
- If I plug both ports of the SAS HBA into the JBOD, I still only see 23 disks in format
- LSI firmware is at default settings
- boot disks are not on LSI controller (onboard AHCI) so rpool isn't involved in this
- OS is OpenSolaris snv_118
I thought that mpxio was disabled by default for SAS, so shouldn't I see 46 disks instead of 23? I don't necessarily want to use mpxio for this setup unless I need to: my goal is to create better bandwidth between the SAS controller and the JBOD and I am not concerned with multipath failover/redundancy. How can I prove that with both ports connected that I am actually using both ports under heavy IO (i.e. scrub)?
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Posts:
3
From:
US
Registered:
10/30/09
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Re: Multipath (mpxio) needed on SAS or not?
Posted:
Nov 3, 2009 4:05 PM
in response to: acheal
To: Communities » storage » discuss
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1. Firstly, you can run " stmsboot -L" to double check if the multipathing is enabled in your box:
# stmsboot -L
stmsboot: MPxIO is not enabled
If MPXIO is disabled, you should see 46 disks.
2. For higher performance, I think you can enable the multipathing, then manual failover so that the different disks are on different ports:
1).Run "mpathadm list " to get all disks
# mpathadm list lu
/dev/rdsk/c0t5000C5000F279C0Bd0s2
Total Path Count: 2
Operational Path Count: 2
2). To pin one disk on one path, you can disable the other path:
# mpathadm show lu /dev/rdsk/c0t5000C5000F279C0Bd0s2
Logical Unit: /dev/rdsk/c0t5000C5000F279C0Bd0s2
mpath-support: libmpscsi_vhci.so
Vendor: SEAGATE
Product: ST373455SS
Revision: 0002
Name Type: unknown type
Name: 5000c5000f279c0b
Asymmetric: no
Current Load Balance: round-robin
Logical Unit Group ID: NA
Auto Failback: on
Auto Probing: NA
Paths:
Initiator Port Name: 500605b000c83ff0
Target Port Name: 5000c5000f279c0a
Override Path: NA
Path State: OK
Disabled: no
Initiator Port Name: 500605b000c837f0
Target Port Name: 5000c5000f279c09
Override Path: NA
Path State: OK
Disabled: no
Target Ports:
Name: 5000c5000f279c0a
Relative ID: 0
Name: 5000c5000f279c09
Relative ID: 0
In my case, if I want this disk stay on first path, then I will disable the second path:
mpathadm disable path -i 500605b000c837f0 -t 5000c5000f279c09 -l /dev/rdsk/c0t5000C5000F279C0Bd0s2
Please note: You need to diable load-balance and auto failback for scsi_vhci. It is in "/kernel/drv/scsi_vhci.conf"
# vi /kernel/drv/scsi_vhci.conf
#
# Load balancing global configuration: setting load-balance="none" will cause
# all I/O to a given device (which supports multipath I/O) to occur via one
# path. Setting load-balance="round-robin" will cause each path to the device
# to be used in turn.
#
load-balance="none";
#
# Automatic failback configuration
# possible values are auto-failback="enable" or auto-failback="disable"
auto-failback="disable";
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Posts:
18
From:
Registered:
6/24/09
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Re: Multipath (mpxio) needed on SAS or not?
Posted:
Nov 4, 2009 11:02 PM
in response to: autumn
To: Communities » storage » discuss
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> 1. Firstly, you can run " stmsboot -L" to double
> check if the multipathing is enabled in your box:
> # stmsboot -L
> stmsboot: MPxIO is not enabled
>
> If MPXIO is disabled, you should see 46 disks.
>
Turns out that the LSI3801E does not support x8 wide paths (i.e. bonding both x4 SAS ports). Since the expander was reporting the same WWN on both ports, the LSI card "hides" the other connection so you only get to use one port/path. The only way around it is to have the expander report two different WWNs on the two ports, which mine doesn't support. If I use two separate controllers, I could do this but I am limited to one PCIe slot, so no go for me unless I move to the 31601E which is hard to find.
Thanks for the info on the multipathing setup though...all good to know. Is enabling "multipathing" in the LSI BIOS a requirement to make this work; by default, this is disabled?
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