Lustre discuss - Apr 2008 - MGS and loop devices

Hello

Has anybody used loop devices for MGT?

Since there''s not so much information stored in this Target, it
can be a good alternative to disk partitions...

But I don''t know which size is sufficient to store configurations
data for several File system.

Does anyone on the list have some information on this topic ?

Thanks in advance,
Jerome

On Mon, 2008-04-14 at 17:40 +0200, Fereyre Jerome wrote:
> Has anybody used loop devices for MGT?
> 
> Since there''s not so much information stored in this Target, it
> can be a good alternative to disk partitions...
> 
You could place it on the same partition/volume as the MDT but I believe
you get less noise in dmesg during start/stop if you have the MGT and
MDT seperate as this allows you to start the MDT after your OSSs.

I''m using an LVM volume for my MGS (and MDT - wanted to try the fast
scanner for backup which requires snapshoting). My MGS size is 64MB -
about 10% is used in a two oss + 3 clients setup. 

I''m also interested in knowing about how much space the MGT uses for a
many-node system.

/Jakob

I don''t know if this still applies, but back when I was doing some  
work with Xen Hypervisor, loopback devices did not provide safe  
places to put files in a power failure.

Loopback did not make sure that things in memory were flushed to the  
file and synced to the disk, leaving dirty data in memory.

Might want to verify this, just don''t get caught with stuff in ram.

Brock Palen
www.umich.edu/~brockp
Center for Advanced Computing
brockp at umich.edu
(734)936-1985



On Apr 14, 2008, at 3:12 PM, Jakob Goldbach wrote:
>
> On Mon, 2008-04-14 at 17:40 +0200, Fereyre Jerome wrote:
>> Has anybody used loop devices for MGT?
>>
>> Since there''s not so much information stored in this Target,
it
>> can be a good alternative to disk partitions...
>>
>
> You could place it on the same partition/volume as the MDT but I  
> believe
> you get less noise in dmesg during start/stop if you have the MGT and
> MDT seperate as this allows you to start the MDT after your OSSs.
>
> I''m using an LVM volume for my MGS (and MDT - wanted to try the
fast
> scanner for backup which requires snapshoting). My MGS size is 64MB -
> about 10% is used in a two oss + 3 clients setup.
>
> I''m also interested in knowing about how much space the MGT uses
for a
> many-node system.
>
> /Jakob
>
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