WRITE_AND_VERIFY doubt

Qi, Yanling Yanling.Qi at lsi.com
Fri May 8 14:05:03 PDT 2009


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r0905086_f.htm">HTML-formatted message</a>

Flavio,
I think I understand your configuration. You have two DS4700 arrays. You
replicate your volumes between the two arrays. Both the primary volumes and
the secondary (the replicated) volumes are visible to your Linux host. The
replicated volume has write-protection. If the Linux host can not access the
primary volumes or a primary volume becomes secondary (due to role switch),
you would like to start your read/write access to your new primary volume.
First, the device-mapper multupathing is not designed for "storage array
failover". The array failover could be handled in the level higher than the
DM-MP or the application level.  Secondly, the replication, most of times, is
for disaster recovery between two sites. I would be interested in your use
case why you would like to have array failover on the same Linux host.
Thanks,
Yanling
________________________________
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Flavio Junior
Sent: Friday, May 08, 2009 1:42 PM
To: t10 at t10.org
Subject: Re: WRITE_AND_VERIFY doubt
Hi Konrad, thanks for your answer, but...
I've already configured multipath to group my 4 paths to same LUN as a single
device, the problem here is about 2 different LUN's.
These LUN's are different because it comes from distinct storages devices, I
want to group both because the contents is being replicated by DS4700
Enhanced Remote Mirror feature.
--
Flávio do Carmo Júnior
Florianópolis/SC, Brazil
On Fri, May 8, 2009 at 1:50 PM, Konrad Rzeszutek
<konrad at virtualiron.com> wrote:
On Fri, May 08, 2009 at 12:52:28PM -0300, Flavio Junior wrote:
> Hi folks, afternoon.
>
> I've a tad doubt when writing a simple code to sends a WRITE_AND_VERIFY
> (0x2E) command to a scsi device.
>
> I need to do it to decide if this is a primary (and read-write) storage or
a
> secundary (and read-only) storage (ibm ds4700), and adjust my I/O MultiPath
I was under the impression that the DS4700 was an RDAC device. Meaning
you can use these settings:
 device {
       vendor	       "IBM"
       product	       "1814"
       hardware_handler    "1 rdac"
       path_grouping_policy    group_by_prio
       prio	       "rdac"
       failback        immediate
       path_checker	   rdac
   }
And it will detect whether your secondary paths are not in usage and
call them 'ghost'.
> priority accordingly, and i need to run it periodically to check if the
> roles change.
>
> My doubt is, is there a area that I cant safety use this command without
> risk to corrupt the data on disk? I'm not a really developer, just make
some
You will cause corruption.
> researches and read some codes to assembly my own, here is the code:
> http://pastebin.com/m22b06f04
>
>
> O course, if there is a way more elegant to get this info I'll appreciate
if
> someone says me. :)
I think using the right multipath.conf entry should do it.
>
>
> Really thanks in advance and some sorries for english and dumb question.
>
>
> --
>
> Flávio do Carmo Jùnior
> Florianopolis/SC, Brazil



More information about the T10 mailing list