EMA question...

[RTMJ]

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.

[skt_skt]

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

[RTMJ]

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 )

[RTMJ]

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?

[skt_skt]

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

[skt_skt]

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??

[Uwe Zessin · Accepted solution]

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!!

[RTMJ]

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?

[Uwe Zessin]

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