IO error issues with MD3000i on Linux

[Scott Ehrlich]

On Fri, Jun 19, 2009 at 4:10 AM, <Shyam_Iyer at dell.com> wrote:
>> -----Original Message-----
>> From: linux-poweredge-bounces at lists.us.dell.com [mailto:linux-
>> poweredge-bounces at lists.us.dell.com] On Behalf Of Scott Ehrlich
>> Sent: Friday, June 19, 2009 6:55 AM
>> To: linux-poweredge-Lists
>> Subject: Re: IO error issues with MD3000i on Linux
>>
>> Here is a basic question -
>>
>> dmesg shows many errors from the md3000i.   Newer kernels treat the
>> "errors" more appropriately.
>>
>
> True. Newer kernels like 2.6.27~ and above have a scsi device handler
> module (scsi_dh_rdac) which can handle active/active, active/passive
> paths effectively.
>
>
>> My question is - are the errors really bad errors?   Is the hardware,
>> or is the data, really in trouble?  Or, are the logged errors simply
>> benign software reports that the kernel and drivers don't know any
>> better how to deal with the responses from the md3000i, but the data
>> and hardware are all fine?
>>
>
> Currently, stock rhel-5.3 has the module backported but without the
> support for the MD3000i device. Patches + kernel fix available in
> bugzilla https://bugzilla.redhat.com/show_bug.cgi?id=487293 for quick
> peak.

I'm currently running 64-bit CentOS 5.2 on an isolated LAN.
Fundamentally, again, is there any actually data loss/corruption - is
there a real data integrity problem - do I have anything to worry
about, or is the software as a while (kernel + drivers) producing
actual data read/write errors, thus an upgrade would be required?

Thanks.

>
> The default path_selector "readsector0" can't make effective decisions
> on active and passive paths.
>
> The right way to do this is possibly load the scsi_dh_rdac module(with
> support for MD3000i) and use the following multipath.conf -
>
> blacklist {
>        device {
>                        vendor                  "DELL"
>                        product                 "Universal Xport"
>                }
>        }
> devices {
>        device {
>                vendor                  "DELL"
>                product                         "MD3000i"
>                getuid_callout          "/sbin/scsi_id -g -u -d
> /block/%n"
>                getuid_callout          "/lib/udev/scsi_id -g -u -d
> /block/%n"
>                prio_callout            "/sbin/mpath_prio_rdac /dev/%n"
>                prio                            rdac
>                features                        "0"
>                hardware_handler                "1 rdac"
>                path_grouping_policy    "group_by_prio"
>                failback                        "immediate"
>                path_checker            "rdac"
>                no_path_retry           queue
>                queue_if_no_path        1
>        }
> }
>
> And finally restart the multipathd.
>
> Please check your paths using "multipath -ll"
>
> -Shyam Iyer
>