[Lustre-discuss] more on MGS and MDT separation

Ms. Megan Larko dobsonunit at gmail.com
Thu Oct 22 12:41:30 PDT 2009


Greetings,

I am deactivating an older Lustre filesystem in favor of a newer one
(already up and stable).
The message in Lustre-discuss Digest Vol 45 Issue 22 stated (with two
of my comments in-line):

Message: 2
Date: Sun, 11 Oct 2009 19:05:07 +0200
From: Bernd Schubert <bs_lists at aakef.fastmail.fm>
Subject: Re: [Lustre-discuss] Moving MGS to separate device
To: lustre-discuss at lists.lustre.org
Message-ID: <200910111905.08076.bs_lists at aakef.fastmail.fm>
Content-Type: Text/Plain;  charset="iso-8859-15"

Hello Wojciech,

I already did this several times, here are the steps I so far used:

1) Remove MGS from MDT-device

tunefs.lustre --nogms /dec/mdt_device
                        ^^^^
          Megan: I am assuming "--nomgs"  here.

2) Create new MGS

mkfs.lustre --mgs /dev/mgs_device

3) Make sure OSTs and  MDTs re-register with the MGS:

tunefs.lustre --writeconf  /dev/device

         Megan:  Do I need to do this even if the MGS is being moved
from a shared device with an MDT to its own device/hard drive on the
same physical server (same MAC addr, IP, hostname etc.....)?

I'm not sure if writeconf is really necessary, but so far I always did it to
make sure everything goes smoothly (clients shouldn't have the filesystem
mounted at this step).

5) Mount MGS, MDT, OSTs

4) Re-apply settings done with lctl.

         Megan: Why are the above ordered the way they are?  Shouldn't
I mount first and then apply the settings?   (I didn't think I could
"lctl" an unmounted OST/MDT etc.)


As you also wrote (private mail), it might be possible to just copy over the
CONFIGS directory, but I never tried to do that.



Hope it helps,
Bernd

     Megan:  Thanks!

Additionally in Lustre-discuss Digest Vol 45 Issue 36 A. Dilger opined:
"...128Mb is the max size the MGS would ever need."

Wow!  That is small.  I know the MGS does not store the sort of data
retained on an MDT for a multi-Tb filesystem, but really 128Mb max
would be used?

Thanks for you advice!
Megan Larko



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