Lustre discuss - Jun 2006 - How Does MDS Distribute Files Over OST Nodes?

Hello!

On Sun, May 28, 2006 at 09:45:23PM -0600, EKC wrote:
> My concern is that these files my be lumped by the MDS onto a few
> OST''s, leading to uneven resource utilization of the OST nodes.
QoS in Lustre 1.6 should address uneven space utilisation.
> My question is: how does the Lustre MDS determine how to allocate
> files colocated within the same directory over the OST''s? Are
files
Files are allocated on allowed OSTs (subject to default striping or
current directory striping (if present) policy) in round-robin manner.
So if you have 3 allowed OSTs, you''d get file 1 on ost 0, file 2 on
ost 1, file 3 on ost 2, file 4 on ost 0, ...
> Lustre MDS evenly distribute them over all of the OST''s? Is there
any
> correlation between the location of a file in the directory tree and
> the OST that it is mapped to?
No, except if some directory has specific striping pattern that only
allows its files to be allocated on certain subset of OSTs.

There is KB article on striping at
https://bugzilla.lustre.org/show_bug.cgi?id=9357

Bye,
    Oleg

Hello,

I''m running 12 OST nodes on a test cluster. My application Lustre
usage pattern calls for accessing several thousand 5-10 megabyte files
located within the same ext3 directory. I am not striping individual
files over multiple OST''s.

My concern is that these files my be lumped by the MDS onto a few
OST''s, leading to uneven resource utilization of the OST nodes.

My question is: how does the Lustre MDS determine how to allocate
files colocated within the same directory over the OST''s? Are files
located within the same directory mapped to the same OST, or does the
Lustre MDS evenly distribute them over all of the OST''s? Is there any
correlation between the location of a file in the directory tree and
the OST that it is mapped to?

Thanks in advance,

EKC