topic Re: EMA question... in Disk Enclosures

EMA question...

RTMJ — Mon, 09 Nov 2009 07:22:41 GMT

At the moment, each storage unit is showing as NOPREFERRED_PATH.

I want to configure the PREFERRED_PATH switch for each storage unit.

I know the command to do so is....
PREFERRED_PATH=OTHER_CONTROLLER
PREFERRED_PATH=THIS_CONTROLLER

but my question is, can this configuration be done online, while the storage unit is still presented to the server?

Or do first I need to unpresent the storage unit from the server?

Any server reboot required?

Please advice.
Thanks in advance.

Re: EMA question...

skt_skt — Tue, 10 Nov 2009 11:52:17 GMT

storage unit? Can you past the o/p you are seeing?

Re: EMA question...

RTMJ — Wed, 11 Nov 2009 06:29:21 GMT

LUN Uses Used by
------------------------------------------------------------------------------

D21 R273
LUN ID: 6000-1FE1-0013-F3C0-0009-1280-4335-0175
NOIDENTIFIER
Switches:
RUN NOWRITE_PROTECT READ_CACHE
READAHEAD_CACHE WRITEBACK_CACHE
MAX_READ_CACHED_TRANSFER_SIZE = 32
MAX_WRITE_CACHED_TRANSFER_SIZE = 32
Access:
03004_1A1, 03004_1B1, 03004_2A2, 03004_2B2
State:
ONLINE to this controller
Not reserved
NOPREFERRED_PATH
Size: 284389034 blocks
Geometry (C/H/S): ( 278813 / 4 / 255 )

Re: EMA question...

RTMJ — Wed, 11 Nov 2009 06:32:54 GMT

Notice the "NOPREFERRED_PATH" entry.

Now, I want to set it to use a preferred path.

So can this be done online while the storage unit is still presented to the server?

Or do first I need to unpresent the storage unit from the server?

Any server reboot required?

Re: EMA question...

skt_skt — Wed, 11 Nov 2009 07:26:36 GMT

is this LUN part of any Volume manager(like LVM, VxVM) and which OS the server where this LUN is asighned?

Re: EMA question...

skt_skt — Wed, 11 Nov 2009 10:16:07 GMT

May be i am askign too much questions :)

Do you have a path management s/w at host side?

Array like EMC Symmetrix is active/active and load will be distributed across all paths. While EMC Clariions works active/passive and we can set a default owner or a preffered path and only those path is used till a fail over.

I dont know how your array works and a preffered path setting is required or not.

So why do you want to set a prefferd path??

Re: EMA question...

Uwe Zessin — Wed, 11 Nov 2009 13:41:03 GMT

This is an active/passive array.

The preferred path can be changed at any time - it is only a hint when both controllers start. An explicit path selection is usually done from the host operating system (which is not mentioned).

It can be changed without a controller restart, but WARNING: THIS MEANS DATA UNAVILABILITY:
> set D21 NORUN
> set D21 PREFERRED_PATH=OTHER_CONTROLLER
> set D21 RUN

AGAIN, THIS MAKES UNIT D21 TEMPORARILY UNAVAILABLE!!

Re: EMA question...

RTMJ — Mon, 30 Nov 2009 03:12:55 GMT

Hi Uwe,

I've read the HSG80 CLI reference guide and it does not say anything about shutting down access to the UNIT when setting the PREFERRED PATH.

Are you 100% sure it cannot be done online?

Re: EMA question...

Uwe Zessin — Mon, 30 Nov 2009 06:58:29 GMT

It's been some time since I tried it, but I am sure:

- you can modify the setting online, but it has no effect until you restart the controllers

- if you want to move the unit online:
-- use a host-based mechanism
--- e.g. Secure Path interface
--- Tru64 has an embedded utility
--- OpenVMS has a DCL command